Could someone please explain why the following doesn't compile with "const" qualifier while it does work without it?

/* test.d */

module test;

mixin template Foo() {
    mixin("@property int bar() const { return foo; }");
}

int foo = 1;

mixin Foo;

unittest {
    assert(foo == bar);
}

> rdmd -main -unittest test.d
test.d-mixin-4(4): Error: function test.Foo!().bar without 'this' cannot be const
test.d(9): Error: mixin test.Foo!() error instantiating

On Monday, 15 December 2014 at 23:14:30 UTC, aldanor wrote:
> Could someone please explain why the following doesn't compile with "const" qualifier while it does work without it?
>
> /* test.d */
>
> module test;
>
> mixin template Foo() {
>     mixin("@property int bar() const { return foo; }");
> }
>
> int foo = 1;
>
> mixin Foo;
>
> unittest {
>     assert(foo == bar);
> }
>
>> rdmd -main -unittest test.d
> test.d-mixin-4(4): Error: function test.Foo!().bar without 'this' cannot be const
> test.d(9): Error: mixin test.Foo!() error instantiating

Has nothing to do with mixin. This produces the same error
message:

@property int bar() const { return foo; }
int foo = 1;
unittest {assert(foo == bar);}

The thing is, free functions cannot be const. In a const method,
what's const is `this`. A free function doesn't have `this`, so
it cannot be const.

On Monday, 15 December 2014 at 23:21:05 UTC, anonymous wrote:
> On Monday, 15 December 2014 at 23:14:30 UTC, aldanor wrote:
>> Could someone please explain why the following doesn't compile with "const" qualifier while it does work without it?
>>
>> /* test.d */
>>
>> module test;
>>
>> mixin template Foo() {
>>    mixin("@property int bar() const { return foo; }");
>> }
>>
>> int foo = 1;
>>
>> mixin Foo;
>>
>> unittest {
>>    assert(foo == bar);
>> }
>>
>>> rdmd -main -unittest test.d
>> test.d-mixin-4(4): Error: function test.Foo!().bar without 'this' cannot be const
>> test.d(9): Error: mixin test.Foo!() error instantiating
>
> Has nothing to do with mixin. This produces the same error
> message:
>
> @property int bar() const { return foo; }
> int foo = 1;
> unittest {assert(foo == bar);}
>
> The thing is, free functions cannot be const. In a const method,
> what's const is `this`. A free function doesn't have `this`, so
> it cannot be const.

Indeed... thanks!