struct Matrix(S, size_t M, size_t N)
{
}

alias Vec3(S) = Matrix!(S, 3, 1);

void main()
{
    import std.stdio;

    writeln(is(Vec3!float == Matrix!(S, 3, 1), S)); // `alias` `S` is defined here
    writeln(is(Matrix!(float, 3, 1) == Matrix!(S, 3, 1), S)); // Error: declaration `S` is already defined
}

Even though the following code compiles.

    writeln(is(Vec3!float == Matrix!(S, 3, 1), S));
    writeln(is(Vec3!float == Matrix!(S, 3, 1), S));

On Thursday, 16 March 2023 at 03:40:04 UTC, Elfstone wrote:

struct Matrix(S, size_t M, size_t N)
{
}

alias Vec3(S) = Matrix!(S, 3, 1);

void main()
{
    import std.stdio;

    writeln(is(Vec3!float == Matrix!(S, 3, 1), S)); // `alias` `S` is defined here
    writeln(is(Matrix!(float, 3, 1) == Matrix!(S, 3, 1), S)); // Error: declaration `S` is already defined
}

    writeln(is(Vec3!float == Matrix!(S, 3, 1), S));
    writeln(is(Vec3!float == Matrix!(S, 3, 1), S));

Oops, the above code compiles, because I added comments!!!

Now this really doesn't compile:

struct Matrix(S, size_t M, size_t N)
{
}

alias Vec3(S) = Matrix!(S, 3, 1);

void main()
{
    import std.stdio;

    writeln(is(Vec3!float == Matrix!(S, 3, 1), S));
    writeln(is(Matrix!(float, 3, 1) == Matrix!(S, 3, 1), S));
}

On Thursday, 16 March 2023 at 03:44:19 UTC, Elfstone wrote:

struct Matrix(S, size_t M, size_t N)
{
}

alias Vec3(S) = Matrix!(S, 3, 1);

void main()
{
    import std.stdio;

    writeln(is(Vec3!float == Matrix!(S, 3, 1), S));
    writeln(is(Matrix!(float, 3, 1) == Matrix!(S, 3, 1), S));
}

Correction.

With or without comments, mostly it doesn't compile, occasionally it does!
I have no idea.

On Thursday, 16 March 2023 at 04:04:51 UTC, Elfstone wrote:

struct Matrix(S, size_t M, size_t N)
{
}

alias Vec3(S) = Matrix!(S, 3, 1);

void main()
{
    import std.stdio;

    writeln(is(Vec3!float == Matrix!(S, 3, 1), S));
    writeln(is(Matrix!(float, 3, 1) == Matrix!(S, 3, 1), S));
}

I can't get it to compile anymore, it must be some mistake from me. Maybe I forgot to save while modifying the code.

So the S declared in is expression can contaminate the scope? Is this supposed to happen?

On Thursday, 16 March 2023 at 04:31:11 UTC, Elfstone wrote:

Never mind, I just found out this is supposed to happen, S is supposed to be available later.

https://dlang.org/spec/expression.html#is-parameter-list