Add templates to meta.transform

source/tanya/meta/transform.d

@@ -5,7 +5,8 @@
 /**
  * Type transformations.
  *
- * Templates in this module applied to a type produce a transformed type.
+ * Templates in this module can be used to modify type qualifiers or transform
+ * types.
  *
  * Copyright: Eugene Wissner 2017.
  * License: $(LINK2 https://www.mozilla.org/en-US/MPL/2.0/,
@@ -16,6 +17,8 @@
  */
 module tanya.meta.transform;
 
+import tanya.meta.traits;
+
 /**
  * Removes any type qualifiers from $(D_PARAM T).
  *
@@ -33,6 +36,8 @@ module tanya.meta.transform;
  *
  * Params:
  *  T = A type.
+ *
+ * Returns: $(D_PARAM T) without any type qualifiers.
  */
 template Unqual(T)
 {
@@ -66,11 +71,15 @@ pure nothrow @safe @nogc unittest
 }
 
 /**
- * If $(D_PARAM T) is an $(D_KEYWORD enum), $(D_INLINECODE OriginalType!T) evaluates to the
+ * If $(D_PARAM T) is an $(D_KEYWORD enum), $(D_INLINECODE OriginalType!T)
- * most base type of that $(D_KEYWORD enum) and to $(D_PARAM T) otherwise.
+ * evaluates to the most base type of that $(D_KEYWORD enum) and to
+ * $(D_PARAM T) otherwise.
  *
  * Params:
  *  T = A type.
+ *
+ * Returns: Base type of the $(D_KEYWORD enum) $(D_PARAM T) or $(D_PARAM T)
+ *          itself.
  */
 template OriginalType(T)
 {
@@ -110,3 +119,273 @@ pure nothrow @safe @nogc unittest
     static assert(is(OriginalType!E4 == bool));
     static assert(is(OriginalType!(const E4) == bool));
 }
+
+/**
+ * Copies constness of $(D_PARAM From) to $(D_PARAM To).
+ *
+ * The following type qualifiers affect the constness and hence are copied:
+ * $(UL
+ *  $(LI const)
+ *  $(LI immutable)
+ *  $(LI inout)
+ *  $(LI inout const)
+ * )
+ *
+ * Params:
+ *  From = Source type.
+ *  To   = Target type.
+ *
+ * Returns: $(D_PARAM To) with the constness of $(D_PARAM From).
+ *
+ * See_Also: $(D_PSYMBOL CopyTypeQualifiers).
+ */
+template CopyConstness(From, To)
+{
+    static if (is(From T == immutable T))
+    {
+        alias CopyConstness = immutable To;
+    }
+    else static if (is(From T == const T) || is(From T == shared const T))
+    {
+        alias CopyConstness = const To;
+    }
+    else static if (is(From T == inout T) || is(From T == shared inout T))
+    {
+        alias CopyConstness = inout To;
+    }
+    else static if (is(From T == inout const T)
+                 || is(From T == shared inout const T))
+    {
+        alias CopyConstness = inout const To;
+    }
+    else
+    {
+        alias CopyConstness = To;
+    }
+}
+
+///
+pure nothrow @safe @nogc unittest
+{
+    static assert(is(CopyConstness!(int, char) == char));
+    static assert(is(CopyConstness!(const int, char) == const char));
+    static assert(is(CopyConstness!(immutable int, char) == immutable char));
+    static assert(is(CopyConstness!(inout int, char) == inout char));
+    static assert(is(CopyConstness!(inout const int, char) == inout const char));
+
+    static assert(is(CopyConstness!(shared int, char) == char));
+    static assert(is(CopyConstness!(shared const int, char) == const char));
+    static assert(is(CopyConstness!(shared inout int, char) == inout char));
+    static assert(is(CopyConstness!(shared inout const int, char) == inout const char));
+
+    static assert(is(CopyConstness!(const int, shared char) == shared const char));
+    static assert(is(CopyConstness!(const int, immutable char) == immutable char));
+    static assert(is(CopyConstness!(immutable int, const char) == immutable char));
+}
+
+/**
+ * Copies type qualifiers of $(D_PARAM From) to $(D_PARAM To).
+ *
+ * Type qualifiers copied are:
+ * $(UL
+ *  $(LI const)
+ *  $(LI immutable)
+ *  $(LI inout)
+ *  $(LI shared)
+ * )
+ * and combinations of these.
+ *
+ * Params:
+ *  From = Source type.
+ *  To   = Target type.
+ *
+ * Returns: $(D_PARAM To) with the type qualifiers of $(D_PARAM From).
+ *
+ * See_Also: $(D_PSYMBOL CopyConstness).
+ */
+template CopyTypeQualifiers(From, To)
+{
+    static if (is(From T == immutable T))
+    {
+        alias CopyTypeQualifiers = immutable To;
+    }
+    else static if (is(From T == const T))
+    {
+        alias CopyTypeQualifiers = const To;
+    }
+    else static if (is(From T == shared T))
+    {
+        alias CopyTypeQualifiers = shared To;
+    }
+    else static if (is(From T == shared const T))
+    {
+        alias CopyTypeQualifiers = shared const To;
+    }
+    else static if (is(From T == inout T))
+    {
+        alias CopyTypeQualifiers = inout To;
+    }
+    else static if (is(From T == shared inout T))
+    {
+        alias CopyTypeQualifiers = shared inout To;
+    }
+    else static if (is(From T == inout const T))
+    {
+        alias CopyTypeQualifiers = inout const To;
+    }
+    else static if (is(From T == shared inout const T))
+    {
+        alias CopyTypeQualifiers = shared inout const To;
+    }
+    else
+    {
+        alias CopyTypeQualifiers = To;
+    }
+}
+
+///
+pure nothrow @safe @nogc unittest
+{
+    static assert(is(CopyTypeQualifiers!(int, char) == char));
+    static assert(is(CopyTypeQualifiers!(const int, char) == const char));
+    static assert(is(CopyTypeQualifiers!(immutable int, char) == immutable char));
+    static assert(is(CopyTypeQualifiers!(inout int, char) == inout char));
+    static assert(is(CopyTypeQualifiers!(inout const int, char) == inout const char));
+
+    static assert(is(CopyTypeQualifiers!(shared int, char) == shared char));
+    static assert(is(CopyTypeQualifiers!(shared const int, char) == shared const char));
+    static assert(is(CopyTypeQualifiers!(shared inout int, char) == shared inout char));
+    static assert(is(CopyTypeQualifiers!(shared inout const int, char) == shared inout const char));
+}
+
+/**
+ * Evaluates to the unsigned counterpart of the integral type $(D_PARAM T) preserving all type qualifiers.
+ * If $(D_PARAM T) is already unsigned, $(D_INLINECODE Unsigned!T) aliases $(D_PARAM T).
+ *
+ * Params:
+ *  T = A type.
+ *
+ * Returns: Unsigned counterpart of $(D_PARAM T).
+ *
+ * See_Also: $(D_PSYMBOL isSigned).
+ */
+template Unsigned(T)
+if (isIntegral!T)
+{
+    alias UnqualedType = Unqual!(OriginalType!T);
+    static if (is(UnqualedType == byte))
+    {
+        alias Unsigned = CopyTypeQualifiers!(T, ubyte);
+    }
+    else static if (is(UnqualedType == short))
+    {
+        alias Unsigned = CopyTypeQualifiers!(T, ushort);
+    }
+    else static if (is(UnqualedType == int))
+    {
+        alias Unsigned = CopyTypeQualifiers!(T, uint);
+    }
+    else static if (is(UnqualedType == long))
+    {
+        alias Unsigned = CopyTypeQualifiers!(T, ulong);
+    }
+    else
+    {
+        alias Unsigned = T;
+    }
+}
+
+///
+pure nothrow @safe @nogc unittest
+{
+    static assert(is(Unsigned!byte == ubyte));
+    static assert(is(Unsigned!short == ushort));
+    static assert(is(Unsigned!int == uint));
+    static assert(is(Unsigned!long == ulong));
+
+    static assert(is(Unsigned!(const byte) == const ubyte));
+    static assert(is(Unsigned!(shared byte) == shared ubyte));
+    static assert(is(Unsigned!(shared const byte) == shared const ubyte));
+
+    static assert(!is(Unsigned!float));
+    static assert(is(Unsigned!ubyte == ubyte));
+}
+
+/**
+ * Evaluates to the signed counterpart of the integral type $(D_PARAM T) preserving all type qualifiers.
+ * If $(D_PARAM T) is already signed, $(D_INLINECODE Signed!T) aliases $(D_PARAM T).
+ *
+ * Params:
+ *  T = A type.
+ *
+ * Returns: Signed counterpart of $(D_PARAM T).
+ *
+ * See_Also: $(D_PSYMBOL isUnsigned).
+ */
+template Signed(T)
+if (isIntegral!T)
+{
+    alias UnqualedType = Unqual!(OriginalType!T);
+    static if (is(UnqualedType == ubyte))
+    {
+        alias Signed = CopyTypeQualifiers!(T, byte);
+    }
+    else static if (is(UnqualedType == ushort))
+    {
+        alias Signed = CopyTypeQualifiers!(T, short);
+    }
+    else static if (is(UnqualedType == uint))
+    {
+        alias Signed = CopyTypeQualifiers!(T, int);
+    }
+    else static if (is(UnqualedType == ulong))
+    {
+        alias Signed = CopyTypeQualifiers!(T, long);
+    }
+    else
+    {
+        alias Signed = T;
+    }
+}
+
+///
+pure nothrow @safe @nogc unittest
+{
+    static assert(is(Signed!ubyte == byte));
+    static assert(is(Signed!ushort == short));
+    static assert(is(Signed!uint == int));
+    static assert(is(Signed!ulong == long));
+
+    static assert(is(Signed!(const ubyte) == const byte));
+    static assert(is(Signed!(shared ubyte) == shared byte));
+    static assert(is(Signed!(shared const ubyte) == shared const byte));
+
+    static assert(!is(Signed!float));
+    static assert(is(Signed!byte == byte));
+}
+
+/**
+ * Retrieves the target type `U` of a pointer `U*`.
+ *
+ * Params:
+ *  T = Pointer type.
+ *
+ * Returns: Pointer target type.
+ */
+template PointerTarget(T)
+if (isPointer!T)
+{
+    static if (is(T U : U*))
+    {
+        alias PointerTarget = U;
+    }
+}
+
+///
+pure nothrow @safe @nogc unittest
+{
+    static assert(is(PointerTarget!(bool*) == bool));
+    static assert(is(PointerTarget!(const bool*) == const bool));
+    static assert(is(PointerTarget!(const shared bool*) == const shared bool));
+    static assert(!is(PointerTarget!bool));
+}