Hi,

I am looking for a method to log the current function name + parameters.
Getting the name of the current function is simply possible with __PRETTY_FUNCTION__
Is there some possibility to generically access the parameters of a function such that they can be iterated and printed out?

currently i have something like this:
log.info(__PRETTY_FUNCTION__,  " ", parameter1, " ", parameter2);

i would like to get to something like that:
log.info(__PRETTY_FUNCTION__,  " ", parameters.join(", "));

On Saturday, 17 March 2018 at 10:34:41 UTC, dom wrote:
> Hi,
>
> I am looking for a method to log the current function name + parameters.
> Getting the name of the current function is simply possible with __PRETTY_FUNCTION__
> Is there some possibility to generically access the parameters of a function such that they can be iterated and printed out?
>
> currently i have something like this:
> log.info(__PRETTY_FUNCTION__,  " ", parameter1, " ", parameter2);
>
> i would like to get to something like that:
> log.info(__PRETTY_FUNCTION__,  " ", parameters.join(", "));

You may be able to do something with a mixin. I tried this but I think I'm hitting a compiler bug, or I'm just using mixins wrong.

import std.stdio;

string arguments(alias f)() {
    import std.meta: AliasSeq;
    import std.traits: ParameterIdentifierTuple;
    import std.array: join;
    string[] args;
    foreach (a; [AliasSeq!(ParameterIdentifierTuple!f)]) {
        args ~= `"` ~ a ~ `: ", ` ~ a;
    }
    return args.join(`, ", ", `);
}

// calling writeln(mixin(arguments!f)) should do what you want.

void f(int a, int b, int c) {

    // But you get a:
    // Error: Using the result of a comma expression is not allowed
    // writeln(mixin(arguments!f));


    auto value = arguments!f; // "a: ", a, ", ", "b: ", b, ", ", "c: ", c
    writeln(value);

    // This is ok:
    writeln("a: ", a, ", ", "b: ", b, ", ", "c: ", c);
}

void main() {
 	f(1, 2, 3);
}

You might be able to start with that and get something that works. Or maybe someone knows how to make the mixin part above compile. I have a feeling you may need to make the arguments() function return a string("p0: ", arg0, ", p1: ", arg1" ...) instead so that it's a full string instead of a comma separated expression maybe.

Cheers

On Sunday, 18 March 2018 at 22:57:15 UTC, aliak wrote:
>     // But you get a:
>     // Error: Using the result of a comma expression is not allowed
>     // writeln(mixin(arguments!f));

You can't mix part of a function call in: "Mixed in text must form complete declarations, statements, or expressions." (https://dlang.org/articles/mixin.html)

In this case, it evaluates to a comma expression, which is deprecated. If you put the "writeln();" inside the mixin string it should form a complete statement and compile.

On Saturday, 17 March 2018 at 10:34:41 UTC, dom wrote:
> Hi,
>
> I am looking for a method to log the current function name + parameters.
> Getting the name of the current function is simply possible with __PRETTY_FUNCTION__
> Is there some possibility to generically access the parameters of a function such that they can be iterated and printed out?
>
> currently i have something like this:
> log.info(__PRETTY_FUNCTION__,  " ", parameter1, " ", parameter2);
>
> i would like to get to something like that:
> log.info(__PRETTY_FUNCTION__,  " ", parameters.join(", "));

You can't get the parameters names at the moment, but there's a PR for it:

https://github.com/dlang/dmd/pull/7821

On Sunday, 18 March 2018 at 23:17:58 UTC, Dennis wrote:
> On Sunday, 18 March 2018 at 22:57:15 UTC, aliak wrote:
>>     // But you get a:
>>     // Error: Using the result of a comma expression is not allowed
>>     // writeln(mixin(arguments!f));
>
> You can't mix part of a function call in: "Mixed in text must form complete declarations, statements, or expressions." (https://dlang.org/articles/mixin.html)
>
> In this case, it evaluates to a comma expression, which is deprecated. If you put the "writeln();" inside the mixin string it should form a complete statement and compile.

Ah! Thanks for the clarification.