Howdy, any idea what Im doing wrong? Given a type T i want to test the presence of certain methods. I looked in phobos to see how isInputRange was defined but it didnt really help as all the methods have no parameters and it used some weird lamda stuff i think.


template isPathType(T)
{
    alias FloatType = ReturnType!(T.x);

    enum isPathType = (isFloatOrDouble!(FloatType)
        && (is(typeof(&T.x) == FloatType delegate(size_t idx)))
        && (is(typeof(&T.y) == FloatType delegate(size_t idx)))
        && (is(typeof(&T.cmd) == PathCmd delegate(size_t idx)))
        && (is(typeof(&T.points) == Point!FloatType delegate(size_t idx)))
        && (is(typeof(&T.length) == size_t delegate())));
}

try changing delegate to function, on the type itself it is often function

On Saturday, 16 May 2020 at 01:11:54 UTC, NaN wrote:
> Howdy, any idea what Im doing wrong? Given a type T i want to test the presence of certain methods. I looked in phobos to see how isInputRange was defined but it didnt really help as all the methods have no parameters and it used some weird lamda stuff i think.
>
>
> template isPathType(T)
> {
>     alias FloatType = ReturnType!(T.x);
>
>     enum isPathType = (isFloatOrDouble!(FloatType)
>         && (is(typeof(&T.x) == FloatType delegate(size_t idx)))
>         && (is(typeof(&T.y) == FloatType delegate(size_t idx)))
>         && (is(typeof(&T.cmd) == PathCmd delegate(size_t idx)))
>         && (is(typeof(&T.points) == Point!FloatType delegate(size_t idx)))
>         && (is(typeof(&T.length) == size_t delegate())));
> }

Rather than trying to inspect the function itself, it's easier to check that the result of *calling* the function is what you expect it to be. So, for example:

    is(typeof(T.x(size_t.init)) == FloatType)

The above checks to see whether, when you call T.x with a size_t argument, you get a FloatType back. If you write your checks this way, it doesn't matter whether T.x is a function, a delegate, or even a template.

On Saturday, 16 May 2020 at 02:02:47 UTC, Paul Backus wrote:
> On Saturday, 16 May 2020 at 01:11:54 UTC, NaN wrote:
>
> Rather than trying to inspect the function itself, it's easier to check that the result of *calling* the function is what you expect it to be. So, for example:
>
>     is(typeof(T.x(size_t.init)) == FloatType)
>
> The above checks to see whether, when you call T.x with a size_t argument, you get a FloatType back. If you write your checks this way, it doesn't matter whether T.x is a function, a delegate, or even a template.

That fixed it. Thanks.