[Issue 15615] New: Creating a Variant with a const primitive type doesn't compile

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=15615

          Issue ID: 15615
           Summary: Creating a Variant with a const primitive type doesn't
                    compile
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Windows
            Status: NEW
          Severity: normal
          Priority: P1
         Component: phobos
          Assignee: nobody at puremagic.com
          Reporter: initrd.gz at gmail.com

Trying to construct a variant with a constant value type (i.e. the value is
copied so the const doesn't matter) fails with a compiler error.

Example:

    import std.variant;

    alias Value = Algebraic!(long, double);

    void main() {
        const long foo = 123L;
        long bar = foo;
        Value baz = Value(foo);
    }

> rdmd ~/test.d
/usr/include/dmd/phobos/std/variant.d(544): Error: static assert  "Cannot store
a const(long) in a VariantN!(8LU, long, double)"
/home/col/test.d(9):        instantiated from here: __ctor!(const(long))
Failed: ["dmd", "-v", "-o-", "/home/col/test.d", "-I/home/col"]

The same issue occurs if `foo` is immutable, or a double or boolean.

However, it does work with structs or slices:

    import std.variant;

    struct MyStruct { int a, b; }

    alias Value = Algebraic!(MyStruct, string);

    void main() {
        const MyStruct foo = MyStruct(1, 2);
        MyStruct bar = foo;
        Value baz = Value(foo);

        const string foo2 = "asdf";
        string bar2 = foo2;
        Value baz2 = Value(foo2);
    }

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