Re: alias to a property as an argument to a mixin template

[Ali Çehreli]

On 09/23/2012 11:49 AM, comco wrote:

For this program I'm getting an "Error: need 'this' to access member x"
at line (*). Does that mean that we cannot alias a property as an
argument of a template mixin?

import std.stdio;

mixin template T(alias a) {
void f() {
writeln(a); // (*)
}
}

struct S {
int x;
}

void main() {
auto s = S(4);
mixin T!(s.x);
f();
}

If I change main() as follows, I still get the same error:

void main1() {
auto s = S(4);
with (s) {
mixin T!(x);
f();
}
}

But now, I can get it working by this trick:

import std.stdio;

mixin template T(alias a) {
void f() {
mixin("writeln(" ~ a.stringof ~ ");");
}
}

struct S {
int x;
}

void main() {
auto s = S(4);
with (s) {
mixin T!(x);
f();
}
} // prints 4

So, using string mixins works, but explicit alias to the property name
seems not to. Why is that and is there any other way of achieving the
result witout using template mixins?

There is also delegates:

import std.stdio;

struct S {
    int x;
}

void main() {
    auto s = S(4);
    auto f = { return s.x; };
    f();
}

Ali