Bug 9166 – std.typecons.Nullable and NullableRef don't work with a not mutable type

import std.typecons: Nullable; void main() { auto n = Nullable!(immutable int)(5); } DMD 2.061alpha gives: ...\dmd2\src\phobos\std\typecons.d(1170): Error: can only initialize const member _value inside constructor test.d(3): Error: template instance std.typecons.Nullable!(immutable(int)) error instantiating The problem is in this part of std.typecons.Nullable: /** Assigns $(D value) to the internally-held state. If the assignment succeeds, $(D this) becomes non-null. */ void opAssign()(T value) { _value = value; _isNull = false; } If I put it inside a "static if" it seems to work: static if (isMutable!T) { /** Assigns $(D value) to the internally-held state. If the assignment succeeds, $(D this) becomes non-null. */ void opAssign()(T value) { _value = value; _isNull = false; } }

See also Issue 9164

The same happens with NullableRef: import std.typecons: NullableRef; alias NII = NullableRef!(immutable int); void main() {} ...\dmd2\src\phobos\std\typecons.d(1451): Error: cannot modify immutable expression *this._value test.d(2): Error: template instance std.typecons.NullableRef!(immutable(int)) error instantiating

Works for me in 2.065