tanya/middle/tanya/meta.d

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/**
 * Template metaprogramming.
 *
 * This package contains utilities to acquire type information at compile-time,
 * to transform from one type to another. It has also different algorithms for
 * iterating, searching and modifying template arguments.
 *
 * Copyright: Eugen Wissner 2017-2026.
 * License: $(LINK2 https://www.mozilla.org/en-US/MPL/2.0/,
 *                  Mozilla Public License, v. 2.0).
 */
module tanya.meta;

import std.meta;
import std.traits;

/**
 * Determines whether $(D_PARAM T) is a wide string, i.e. consists of
 * $(D_KEYWORD dchar).
 *
 * The character type of the string and the string itself can have any type
 * qualifiers.
 *
 * Static $(D_KEYWORD dchar) arrays are not considered strings.
 *
 * Params:
 *  T = A type.
 *
 * Returns: $(D_KEYWORD true) if $(D_PARAM T) is a wide string,
 *          $(D_KEYWORD false) otherwise.
 */
enum bool isWideString(T) = is(immutable T == immutable dchar[]);

///
@nogc nothrow pure @safe unittest
{
    static assert(isWideString!(dchar[]));
    static assert(!isWideString!(char[]));
    static assert(!isWideString!(wchar[]));

    static assert(isWideString!dstring);
    static assert(!isWideString!string);
    static assert(!isWideString!wstring);

    static assert(isWideString!(const dstring));
    static assert(!isWideString!(const string));
    static assert(!isWideString!(const wstring));

    static assert(isWideString!(shared dstring));
    static assert(!isWideString!(shared string));
    static assert(!isWideString!(shared wstring));

    static assert(isWideString!(const(dchar)[]));
    static assert(isWideString!(inout(dchar)[]));
    static assert(isWideString!(shared(const(dchar))[]));
    static assert(isWideString!(shared(dchar)[]));
    static assert(!isWideString!(dchar[10]));
}

/*
 * Tests whether $(D_PARAM T) is an interface.
 *
 * Params:
 *  T = A type.
 *
 * Returns: $(D_KEYWORD true) if $(D_PARAM T) is an interface,
 *          $(D_KEYWORD false) otherwise.
 */
private enum bool isInterface(T) = is(T == interface);

/**
 * Determines whether $(D_PARAM T) is a polymorphic type, i.e. a
 * $(D_KEYWORD class) or an $(D_KEYWORD interface).
 *
 * Params:
 *  T = A type.
 *
 * Returns: $(D_KEYWORD true) if $(D_PARAM T) is a $(D_KEYWORD class) or an
 *          $(D_KEYWORD interface), $(D_KEYWORD false) otherwise.
 */
enum bool isPolymorphicType(T) = is(T == class) || is(T == interface);

///
@nogc nothrow pure @safe unittest
{
    interface I
    {
    }
    static assert(isPolymorphicType!Object);
    static assert(isPolymorphicType!I);
    static assert(!isPolymorphicType!short);
}

/**
 * Returns the size in bytes of the state that needs to be allocated to hold an
 * object of type $(D_PARAM T).
 *
 * There is a difference between the `.sizeof`-property and
 * $(D_PSYMBOL stateSize) if $(D_PARAM T) is a class or an interface.
 * `T.sizeof` is constant on the given architecture then and is the same as
 * `size_t.sizeof` and `ptrdiff_t.sizeof`. This is because classes and
 * interfaces are reference types and `.sizeof` returns the size of the
 * reference which is the same as the size of a pointer. $(D_PSYMBOL stateSize)
 * returns the size of the instance itself.
 *
 * The size of a dynamic array is `size_t.sizeof * 2` since a dynamic array
 * stores its length and a data pointer. The size of the static arrays is
 * calculated differently since they are value types. It is the array length
 * multiplied by the element size.
 *
 * `stateSize!void` is `1` since $(D_KEYWORD void) is mostly used as a synonym
 * for $(D_KEYWORD byte)/$(D_KEYWORD ubyte) in `void*`.
 *
 * Params:
 *  T = Object type.
 *
 * Returns: Size of an instance of type $(D_PARAM T).
 */
template stateSize(T)
{
    static if (isPolymorphicType!T)
    {
        enum size_t stateSize = __traits(classInstanceSize, T);
    }
    else
    {
        enum size_t stateSize = T.sizeof;
    }
}

///
@nogc nothrow pure @safe unittest
{
    static assert(stateSize!int == 4);
    static assert(stateSize!bool == 1);
    static assert(stateSize!(int[]) == (size_t.sizeof * 2));
    static assert(stateSize!(short[3]) == 6);

    static struct Empty
    {
    }
    static assert(stateSize!Empty == 1);
    static assert(stateSize!void == 1);
}

/**
 * Finds the minimum value in $(D_PARAM Args) according to $(D_PARAM pred).
 *
 * $(D_PARAM Args) should contain at least one element.
 *
 * $(D_PARAM pred) can evaluate to:
 * $(UL
 *  $(LI $(D_KEYWORD bool): $(D_KEYWORD true) means
 *       $(D_INLINECODE Args[0] < Args[1]).)
 *  $(LI $(D_KEYWORD int): a negative number means that
 *       $(D_INLINECODE Args[0] < Args[1]), a positive number that
 *       $(D_INLINECODE Args[0] > Args[1]), `0` if they equal.)
 * )
 *
 * Params:
 *  pred = Template predicate.
 *  Args = Elements for which you want to find the minimum value.
 *
 * Returns: The minimum.
 *
 * See_Also: $(D_PSYMBOL isLess).
 */
template Min(alias pred, Args...)
if (Args.length > 0 && __traits(isTemplate, pred))
{
    static if (Args.length == 1)
    {
        alias Min = Alias!(Args[0]);
    }
    else static if (isLess!(pred, Args[1], Args[0]))
    {
        alias Min = Min!(pred, Args[1], Args[2 .. $]);
    }
    else
    {
        alias Min = Min!(pred, Args[0], Args[2 .. $]);
    }
}

///
@nogc nothrow pure @safe unittest
{
    enum bool cmp(alias T, alias U) = T < U;
    static assert(Min!(cmp, 8, 4, 5, 3, 13) == 3);
    static assert(Min!(cmp, 8) == 8);
}

/**
 * Finds the maximum value in $(D_PARAM Args) according to $(D_PARAM pred).
 *
 * $(D_PARAM Args) should contain at least one element.
 *
 * $(D_PARAM pred) can evaluate to:
 * $(UL
 *  $(LI $(D_KEYWORD bool): $(D_KEYWORD true) means
 *       $(D_INLINECODE Args[0] < Args[1]).)
 *  $(LI $(D_KEYWORD int): a negative number means that
 *       $(D_INLINECODE Args[0] < Args[1]), a positive number that
 *       $(D_INLINECODE Args[0] > Args[1]), `0` if they equal.)
 * )
 *
 * Params:
 *  pred = Template predicate.
 *  Args = Elements for which you want to find the maximum value.
 *
 * Returns: The maximum.
 *
 * See_Also: $(D_PSYMBOL isLess).
 */
template Max(alias pred, Args...)
if (Args.length > 0 && __traits(isTemplate, pred))
{
    static if (Args.length == 1)
    {
        alias Max = Alias!(Args[0]);
    }
    else static if (isGreater!(pred, Args[1], Args[0]))
    {
        alias Max = Max!(pred, Args[1], Args[2 .. $]);
    }
    else
    {
        alias Max = Max!(pred, Args[0], Args[2 .. $]);
    }
}

///
@nogc nothrow pure @safe unittest
{
    enum bool cmp(alias T, alias U) = T < U;
    static assert(Max!(cmp, 8, 4, 5, 3, 13) == 13);
    static assert(Max!(cmp, 8) == 8);
}

/**
 * Zips one or more $(D_PSYMBOL Pack)s with $(D_PARAM f).
 *
 * Given $(D_PARAM f) and tuples t1, t2, ..., tk, where tk[i] denotes the
 * $(I i)-th element of the tuple $(I k)-th tuple, $(D_PSYMBOL ZipWith)
 * produces a sequence:
 *
 * ---
 * f(t1[0], t2[0], ... tk[0]),
 * f(t1[1], t2[1], ... tk[1]),
 * ...
 * f(tk[0], tk[1], ... tk[i]),
 * ---
 *
 * $(D_PSYMBOL ZipWith) begins with the first elements from $(D_PARAM Packs)
 * and applies $(D_PARAM f) to them, then it takes the second
 * ones and does the same, and so on.
 *
 * If not all argument tuples have the same length, $(D_PSYMBOL ZipWith) will
 * zip only `n` elements from each tuple, where `n` is the length of the
 * shortest tuple in the argument list. Remaining elements in the longer tuples
 * are just ignored.
 *
 * Params:
 *  f      = Some template that can be applied to the elements of
 *           $(D_PARAM Packs).
 *  Packs  = $(D_PSYMBOL Pack) instances.
 *
 * Returns: A sequence, whose $(I i)-th element contains the $(I i)-th element
 *          from each of the $(D_PARAM Packs).
 */
template ZipWith(alias f, Packs...)
if (Packs.length > 0
 && __traits(isTemplate, f)
 && (allSatisfy!(ApplyLeft!(isInstanceOf, Pack), Packs)
 || allSatisfy!(ApplyLeft!(isInstanceOf, Tuple), Packs)))
{
    private template GetIth(size_t i, Args...)
    {
        static if ((Args.length == 0) || (Args[0].Seq.length <= i))
        {
            alias GetIth = AliasSeq!();
        }
        else
        {
            alias GetIth = AliasSeq!(Args[0].Seq[i], GetIth!(i, Args[1 .. $]));
        }
    }
    private template Iterate(size_t i, Args...)
    {
        alias Pack = GetIth!(i, Args);

        static if (Pack.length < Packs.length)
        {
            alias Iterate = AliasSeq!();
        }
        else
        {
            alias Iterate = AliasSeq!(f!Pack, Iterate!(i + 1, Args));
        }
    }
    alias ZipWith = Iterate!(0, Packs);
}

///
@nogc nothrow pure @safe unittest
{
    alias Result1 = ZipWith!(AliasSeq, Pack!(1, 2), Pack!(5, 6), Pack!(9, 10));
    static assert(Result1 == AliasSeq!(1, 5, 9, 2, 6, 10));

    alias Result2 = ZipWith!(AliasSeq, Pack!(1, 2, 3), Pack!(4, 5));
    static assert(Result2 == AliasSeq!(1, 4, 2, 5));

    alias Result3 = ZipWith!(AliasSeq, Pack!(), Pack!(4, 5));
    static assert(Result3.length == 0);
}

/**
 * Holds a typed sequence of template parameters.
 *
 * Different than $(D_PSYMBOL AliasSeq), $(D_PSYMBOL Pack) doesn't unpack
 * its template parameters automatically. Consider:
 *
 * ---
 * template A(Args...)
 * {
 *   static assert(Args.length == 4);
 * }
 *
 * alias AInstance = A!(AliasSeq!(int, uint), AliasSeq!(float, double));
 * ---
 *
 * Using $(D_PSYMBOL AliasSeq) template `A` gets 4 parameters instead of 2,
 * because $(D_PSYMBOL AliasSeq) is just an alias for its template parameters.
 *
 * With $(D_PSYMBOL Pack) it is possible to pass distinguishable
 * sequences of parameters to a template. So:
 *
 * ---
 * template B(Args...)
 * {
 *   static assert(Args.length == 2);
 * }
 *
 * alias BInstance = B!(Pack!(int, uint), Pack!(float, double));
 * ---
 *
 * Params:
 *  Args = Elements of this $(D_PSYMBOL Pack).
 *
 * See_Also: $(D_PSYMBOL AliasSeq).
 */
struct Pack(Args...)
{
    /// Elements in this tuple as $(D_PSYMBOL AliasSeq).
    alias Seq = Args;

    /// The length of the tuple.
    enum size_t length = Args.length;

    alias Seq this;
}

///
@nogc nothrow pure @safe unittest
{
    alias A = Pack!short;
    alias B = Pack!(3, 8, 9);
    alias C = Pack!(A, B);

    static assert(C.length == 2);

    static assert(A.length == 1);
    static assert(is(A.Seq == AliasSeq!short));
    static assert(B.length == 3);
    static assert(B.Seq == AliasSeq!(3, 8, 9));

    alias D = Pack!();
    static assert(D.length == 0);
    static assert(is(D.Seq == AliasSeq!()));
}

/**
 * Unordered sequence of unique aliases.
 *
 * $(D_PARAM Args) can contain duplicates, but they will be filtered out, so
 * $(D_PSYMBOL Set) contains only unique items. $(D_PSYMBOL isEqual) is used
 * for determining if two items are equal.
 *
 * Params:
 *  Args = Elements of this $(D_PSYMBOL Set).
 */
struct Set(Args...)
{
    /// Elements in this set as $(D_PSYMBOL AliasSeq).
    alias Seq = NoDuplicates!Args;

    /// The length of the set.
    enum size_t length = Seq.length;

    alias Seq this;
}

///
@nogc nothrow pure @safe unittest
{
    alias S1 = Set!(int, 5, 5, int, 4);
    static assert(S1.length == 3);
}

/**
 * Produces a $(D_PSYMBOL Set) containing all elements of the given
 * $(D_PARAM Sets).
 *
 * Params:
 *  Sets = List of $(D_PSYMBOL Set) instances.
 *
 * Returns: Set-theoretic union of all $(D_PARAM Sets).
 *
 * See_Also: $(D_PSYMBOL Set).
 */
template Union(Sets...)
if (allSatisfy!(ApplyLeft!(isInstanceOf, Set), Sets))
{
    private template Impl(Sets...)
    {
        static if (Sets.length == 0)
        {
            alias Impl = AliasSeq!();
        }
        else
        {
            alias Impl = AliasSeq!(Sets[0].Seq, Impl!(Sets[1 .. $]));
        }
    }
    alias Union = Set!(Impl!Sets);
}

///
@nogc nothrow pure @safe unittest
{
    alias S1 = Set!(2, 5, 8, 4);
    alias S2 = Set!(3, 8, 4, 1);
    static assert(Union!(S1, S2).Seq == AliasSeq!(2, 5, 8, 4, 3, 1));
}

/**
 * Produces a $(D_PSYMBOL Set) that containing elements of
 * $(D_INLINECODE Sets[0]) that are also elements of all other sets in
 * $(D_PARAM Sets).
 *
 * Params:
 *  Sets = List of $(D_PSYMBOL Set) instances.
 *
 * Returns: Set-theoretic intersection of all $(D_PARAM Sets).
 *
 * See_Also: $(D_PSYMBOL Set).
 */
template Intersection(Sets...)
if (allSatisfy!(ApplyLeft!(isInstanceOf, Set), Sets))
{
    private template Impl(Args...)
    if (Args.length > 0)
    {
        alias Equal = ApplyLeft!(isEqual, Args[0]);
        static if (Args.length == 1)
        {
            enum bool Impl = true;
        }
        else static if (!anySatisfy!(Equal, Args[1].Seq))
        {
            enum bool Impl = false;
        }
        else
        {
            enum bool Impl = Impl!(Args[0], Args[2 .. $]);
        }
    }

    private enum bool FilterImpl(Args...) = Impl!(Args[0], Sets[1 .. $]);

    static if (Sets.length == 0)
    {
        alias Intersection = Set!();
    }
    else
    {
        alias Intersection = Set!(Filter!(FilterImpl, Sets[0].Seq));
    }
}

///
@nogc nothrow pure @safe unittest
{
    alias S1 = Set!(2, 5, 8, 4);
    alias S2 = Set!(3, 8, 4, 1);
    static assert(Intersection!(S1, S2).Seq == AliasSeq!(8, 4));

    static assert(Intersection!(S1).Seq == AliasSeq!(2, 5, 8, 4));
    static assert(Intersection!().length == 0);
}

/**
 * Produces a $(D_PSYMBOL Set) that contains all elements of
 * $(D_PARAM S1) that are not members of $(D_PARAM S2).
 *
 * Params:
 *  S1 = A $(D_PSYMBOL Set).
 *  S2 = A $(D_PSYMBOL Set).
 *
 * Returns: Set-theoretic difference of two sets $(D_PARAM S1) and
 *          $(D_PARAM S2).
 *
 * See_Also: $(D_PSYMBOL Set).
 */
template Difference(alias S1, alias S2)
if (isInstanceOf!(Set, S1) && isInstanceOf!(Set, S2))
{
    private template Impl(Args...)
    {
        alias Equal = ApplyLeft!(isEqual, Args[0]);
        enum bool Impl = !anySatisfy!(Equal, S2.Seq);
    }

    static if (S1.length == 0)
    {
        alias Difference = Set!();
    }
    else static if (S2.length == 1)
    {
        alias Difference = S1;
    }
    else
    {
        alias Difference = Set!(Filter!(Impl, S1.Seq));
    }
}

///
@nogc nothrow pure @safe unittest
{
    alias S1 = Set!(2, 5, 8, 4);
    alias S2 = Set!(3, 8, 4, 1);
    static assert(Difference!(S1, S2).Seq == AliasSeq!(2, 5));
    static assert(Difference!(S2, S1).Seq == AliasSeq!(3, 1));
    static assert(Difference!(S1, Set!()).Seq == AliasSeq!(2, 5, 8, 4));
}

/**
 * Tests whether $(D_INLINECODE Args[0]) is less than or equal to
 * $(D_INLINECODE Args[1]) according to $(D_PARAM cmp).
 *
 * $(D_PARAM cmp) can evaluate to:
 * $(UL
 *  $(LI $(D_KEYWORD bool): $(D_KEYWORD true) means
 *       $(D_INLINECODE Args[0] < Args[1]).)
 *  $(LI $(D_KEYWORD int): a negative number means that
 *       $(D_INLINECODE Args[0] < Args[1]), a positive number that
 *       $(D_INLINECODE Args[0] > Args[1]), `0` if they equal.)
 * )
 *
 * Params:
 *  Args = Two aliases to compare for equality.
 *
 * Returns: $(D_KEYWORD true) if $(D_INLINECODE Args[0]) is less than or equal
 *          to $(D_INLINECODE Args[1]), $(D_KEYWORD false) otherwise.
 */
template isLessEqual(alias cmp, Args...)
if (Args.length == 2 && __traits(isTemplate, cmp))
{
    private enum result = cmp!(Args[1], Args[0]);
    static if (is(typeof(result) == bool))
    {
        enum bool isLessEqual = !result;
    }
    else
    {
        enum bool isLessEqual = result >= 0;
    }
}

///
@nogc nothrow pure @safe unittest
{
    enum bool boolCmp(T, U) = T.sizeof < U.sizeof;
    static assert(isLessEqual!(boolCmp, byte, int));
    static assert(isLessEqual!(boolCmp, uint, int));
    static assert(!isLessEqual!(boolCmp, long, int));

    enum ptrdiff_t intCmp(T, U) = T.sizeof - U.sizeof;
    static assert(isLessEqual!(intCmp, byte, int));
    static assert(isLessEqual!(intCmp, uint, int));
    static assert(!isLessEqual!(intCmp, long, int));
}

/**
 * Tests whether $(D_INLINECODE Args[0]) is greater than or equal to
 * $(D_INLINECODE Args[1]) according to $(D_PARAM cmp).
 *
 * $(D_PARAM cmp) can evaluate to:
 * $(UL
 *  $(LI $(D_KEYWORD bool): $(D_KEYWORD true) means
 *       $(D_INLINECODE Args[0] < Args[1]).)
 *  $(LI $(D_KEYWORD int): a negative number means that
 *       $(D_INLINECODE Args[0] < Args[1]), a positive number that
 *       $(D_INLINECODE Args[0] > Args[1]), `0` if they equal.)
 * )
 *
 * Params:
 *  Args = Two aliases to compare for equality.
 *
 * Returns: $(D_KEYWORD true) if $(D_INLINECODE Args[0]) is greater than or
 *          equal to $(D_INLINECODE Args[1]), $(D_KEYWORD false) otherwise.
 */
template isGreaterEqual(alias cmp, Args...)
if (Args.length == 2 && __traits(isTemplate, cmp))
{
    private enum result = cmp!Args;
    static if (is(typeof(result) == bool))
    {
        enum bool isGreaterEqual = !result;
    }
    else
    {
        enum bool isGreaterEqual = result >= 0;
    }
}

///
@nogc nothrow pure @safe unittest
{
    enum bool boolCmp(T, U) = T.sizeof < U.sizeof;
    static assert(!isGreaterEqual!(boolCmp, byte, int));
    static assert(isGreaterEqual!(boolCmp, uint, int));
    static assert(isGreaterEqual!(boolCmp, long, int));

    enum ptrdiff_t intCmp(T, U) = T.sizeof - U.sizeof;
    static assert(!isGreaterEqual!(intCmp, byte, int));
    static assert(isGreaterEqual!(intCmp, uint, int));
    static assert(isGreaterEqual!(intCmp, long, int));
}

/**
 * Tests whether $(D_INLINECODE Args[0]) is less than
 * $(D_INLINECODE Args[1]) according to $(D_PARAM cmp).
 *
 * $(D_PARAM cmp) can evaluate to:
 * $(UL
 *  $(LI $(D_KEYWORD bool): $(D_KEYWORD true) means
 *       $(D_INLINECODE Args[0] < Args[1]).)
 *  $(LI $(D_KEYWORD int): a negative number means that
 *       $(D_INLINECODE Args[0] < Args[1]), a positive number that
 *       $(D_INLINECODE Args[0] > Args[1]), `0` if they equal.)
 * )
 *
 * Params:
 *  Args = Two aliases to compare for equality.
 *
 * Returns: $(D_KEYWORD true) if $(D_INLINECODE Args[0]) is less than
 *          $(D_INLINECODE Args[1]), $(D_KEYWORD false) otherwise.
 */
template isLess(alias cmp, Args...)
if (Args.length == 2 && __traits(isTemplate, cmp))
{
    private enum result = cmp!Args;
    static if (is(typeof(result) == bool))
    {
        enum bool isLess = result;
    }
    else
    {
        enum bool isLess = result < 0;
    }
}

///
@nogc nothrow pure @safe unittest
{
    enum bool boolCmp(T, U) = T.sizeof < U.sizeof;
    static assert(isLess!(boolCmp, byte, int));
    static assert(!isLess!(boolCmp, uint, int));
    static assert(!isLess!(boolCmp, long, int));

    enum ptrdiff_t intCmp(T, U) = T.sizeof - U.sizeof;
    static assert(isLess!(intCmp, byte, int));
    static assert(!isLess!(intCmp, uint, int));
    static assert(!isLess!(intCmp, long, int));
}

/**
 * Tests whether $(D_INLINECODE Args[0]) is greater than
 * $(D_INLINECODE Args[1]) according to $(D_PARAM cmp).
 *
 * $(D_PARAM cmp) can evaluate to:
 * $(UL
 *  $(LI $(D_KEYWORD bool): $(D_KEYWORD true) means
 *       $(D_INLINECODE Args[0] < Args[1]).)
 *  $(LI $(D_KEYWORD int): a negative number means that
 *       $(D_INLINECODE Args[0] < Args[1]), a positive number that
 *       $(D_INLINECODE Args[0] > Args[1]), `0` if they equal.)
 * )
 *
 * Params:
 *  Args = Two aliases to compare for equality.
 *
 * Returns: $(D_KEYWORD true) if $(D_INLINECODE Args[0]) is greater than
 *          $(D_INLINECODE Args[1]), $(D_KEYWORD false) otherwise.
 */
template isGreater(alias cmp, Args...)
if (Args.length == 2 && __traits(isTemplate, cmp))
{
    private enum result = cmp!Args;
    static if (is(typeof(result) == bool))
    {
        enum bool isGreater = !result && cmp!(Args[1], Args[0]);
    }
    else
    {
        enum bool isGreater = result > 0;
    }
}

///
@nogc nothrow pure @safe unittest
{
    enum bool boolCmp(T, U) = T.sizeof < U.sizeof;
    static assert(!isGreater!(boolCmp, byte, int));
    static assert(!isGreater!(boolCmp, uint, int));
    static assert(isGreater!(boolCmp, long, int));

    enum ptrdiff_t intCmp(T, U) = T.sizeof - U.sizeof;
    static assert(!isGreater!(intCmp, byte, int));
    static assert(!isGreater!(intCmp, uint, int));
    static assert(isGreater!(intCmp, long, int));
}

/**
 * Tests whether $(D_INLINECODE Args[0]) is equal to $(D_INLINECODE Args[1]).
 *
 * $(D_PSYMBOL isEqual) checks first if $(D_PARAM Args) can be compared directly. If not, they are compared as types:
 * $(D_INLINECODE is(Args[0] == Args[1])). It it fails, the arguments are
 * considered to be not equal.
 *
 * If two items cannot be compared (for example comparing a type with a
 * number), they are considered not equal.
 *
 * Params:
 *  Args = Two aliases to compare for equality.
 *
 * Returns: $(D_KEYWORD true) if $(D_INLINECODE Args[0]) is equal to
 *          $(D_INLINECODE Args[1]), $(D_KEYWORD false) otherwise.
 */
template isEqual(Args...)
if (Args.length == 2)
{
    static if ((is(typeof(Args[0] == Args[1])) && (Args[0] == Args[1]))
            || (isTypeTuple!Args && is(Args[0] == Args[1]))
            || __traits(isSame, Args[0], Args[1]))
    {
        enum bool isEqual = true;
    }
    else
    {
        enum bool isEqual = false;
    }
}

///
@nogc nothrow pure @safe unittest
{
    static assert(isEqual!(int, int));
    static assert(isEqual!(8, 8));
    static assert(!isEqual!(int, const(int)));
    static assert(!isEqual!(5, int));
    static assert(!isEqual!(5, 8));
}

/**
 * Tests whether $(D_INLINECODE Args[0]) isn't equal to
 * $(D_INLINECODE Args[1]).
 *
 * $(D_PSYMBOL isNotEqual) checks first if $(D_PARAM Args) can be compared directly. If not, they are compared as types:
 * $(D_INLINECODE is(Args[0] == Args[1])). It it fails, the arguments are
 * considered to be not equal.
 *
 * Params:
 *  Args = Two aliases to compare for equality.
 *
 * Returns: $(D_KEYWORD true) if $(D_INLINECODE Args[0]) isn't equal to
 *          $(D_INLINECODE Args[1]), $(D_KEYWORD false) otherwise.
 */
template isNotEqual(Args...)
if (Args.length == 2)
{
    enum bool isNotEqual = !isEqual!Args;
}

///
@nogc nothrow pure @safe unittest
{
    static assert(!isNotEqual!(int, int));
    static assert(isNotEqual!(5, int));
    static assert(isNotEqual!(5, 8));
}

/**
 * Looks for $(D_PARAM T) in $(D_PARAM L) and returns $(D_KEYWORD true) if it
 * could be found and $(D_KEYWORD false) otherwise.
 *
 * Params:
 *  T = The item to search for.
 *  L = Symbol sequence.
 *
 * Returns: $(D_KEYWORD true) if $(D_PARAM T) can be found in $(D_PARAM L),
 *          $(D_KEYWORD false) otherwise.
 */
enum bool canFind(T, L...) = staticIndexOf!(T, L) != -1;

/// ditto
enum bool canFind(alias T, L...) = staticIndexOf!(T, L) != -1;

///
@nogc nothrow pure @safe unittest
{
    static assert(!canFind!(int));
    static assert(canFind!(int, int));
    static assert(canFind!(int, float, double, int, real));
    static assert(canFind!(3, () {}, uint, 5, 3));
}

/*
 * Tests whether $(D_PARAM T) is a template.
 *
 * $(D_PSYMBOL isTemplate) isn't $(D_KEYWORD true) for template instances,
 * since the latter already represent some type. Only not instantiated
 * templates, i.e. that accept some template parameters, are considered
 * templates.
 *
 * Params:
 *  T = A symbol.
 *
 * Returns: $(D_KEYWORD true) if $(D_PARAM T) is a template,
 *          $(D_KEYWORD false) otherwise.
 */
enum bool isTemplate(alias T) = __traits(isTemplate, T);

///
@nogc nothrow pure @safe unittest
{
    static struct S(T)
    {
    }
    static assert(isTemplate!S);
    static assert(!isTemplate!(S!int));
}

/**
 * Attaches a numeric index to each element from $(D_PARAM Args).
 *
 * $(D_PSYMBOL EnumerateFrom) returns a sequence of tuples ($(D_PSYMBOL Pack)s)
 * consisting of the index of each element and the element itself.
 *
 * Params:
 *  start = Enumeration initial value.
 *  Args  = Enumerated sequence.
 *
 * See_Also: $(D_PSYMBOL Enumerate).
 */
template EnumerateFrom(size_t start, Args...)
{
    static if (Args.length == 0)
    {
        alias EnumerateFrom = AliasSeq!();
    }
    else
    {
        alias EnumerateFrom = AliasSeq!(Pack!(start, Args[0]), EnumerateFrom!(start + 1, Args[1 .. $]));
    }
}

///
@nogc nothrow pure @safe unittest
{
    static assert(EnumerateFrom!(0, int, uint, bool).length == 3);
}

///
@nogc nothrow pure @safe unittest
{
    alias Expected = AliasSeq!(Pack!(cast(size_t) 0, int),
                               Pack!(cast(size_t) 1, uint));
    static assert(is(EnumerateFrom!(0, int, uint) == Expected));
}

/**
 * Attaches a numeric index to each element from $(D_PARAM Args).
 *
 * $(D_PSYMBOL EnumerateFrom) returns a sequence of tuples ($(D_PSYMBOL Pack)s)
 * consisting of the index of each element and the element itself.
 *
 * Params:
 *  Args  = Enumerated sequence.
 *
 * See_Also: $(D_PSYMBOL EnumerateFrom).
 */
alias Enumerate(Args...) = EnumerateFrom!(0, Args);

///
@nogc nothrow pure @safe unittest
{
    alias Expected = AliasSeq!(Pack!(cast(size_t) 0, int),
                               Pack!(cast(size_t) 1, uint));
    static assert(is(Enumerate!(int, uint) == Expected));
}