• Heromyth (42/42) May 10 2020 I want to get the UDAs for for a function parameter. Here the
• Adam D. Ruppe (19/21) May 10 2020 I think my blog aside is one of the few if only write-ups on how
• Heromyth (45/67) May 10 2020 That's great! It should use

Heromyth <bitworld qq.com> writes:

I want to get the UDAs for for a function parameter. Here the 
test code and I got some errors:

source/app.d(29,33): Error: first argument is not a symbol
source/app.d(39,15): Error: template instance app.test!(ClassA) 
error instantiating

How can I fix this? Would this be a bug? Thanks.

=====================
import std.stdio;
import std.traits;
import std.meta;


struct Length {
     int a;
     int b;
}

class ClassA {
     void test( Length(1, 9) int len,  Length(2, 4) int size) {
         writeln("It's OK");
     }

     void test(string name) {
         writeln("Can't be compiled");
     }
}

string test(T)() {
     string str;
     alias currentMembers = __traits(getOverloads, T, "test");

     static foreach(member; currentMembers) {{
         alias Params = Parameters!(member);
         static foreach(i; 0 .. Params.length)
         {{
             alias ThisParameter =  Params[i .. i + 1];
             static foreach(uda; __traits(getAttributes, 
ThisParameter)) {
                 str ~= uda.stringof ~  "\n";
             }
         }}
     }}

     return str;
}

void main() {
     enum aa = test!(ClassA);
     writeln(aa);
}

Adam D. Ruppe <destructionator gmail.com> writes:

On Monday, 11 May 2020 at 02:25:39 UTC, Heromyth wrote:
 I want to get the UDAs for for a function parameter. Here the 
 test code and I got some errors:

I think my blog aside is one of the few if only write-ups on how 
to do this:

http://dpldocs.info/this-week-in-d/Blog.Posted_2019_02_11.html#how-to-get-uda-on-a-function-param


the library will not help much, you need to slice the parameters 
yourself. (It might work combine lib stuff with slice though, 
e.g. getUDA!(Parameters!F[1 .. 2]) maybe, i have never tried).

but this does work:

         static if(is(typeof(method) P == __parameters))
         foreach(idx, _; P) {{
		// alias for convenience later
                 alias param = P[idx .. idx + 1]; // this slice is 
the trick
		// can get the identifier now
                 string ident = __traits(identifier, param);
		// and the attributes
                 foreach(attr; __traits(getAttributes, param))
			{}
	}}

Heromyth <bitworld qq.com> writes:

On Monday, 11 May 2020 at 02:34:32 UTC, Adam D. Ruppe wrote:
 On Monday, 11 May 2020 at 02:25:39 UTC, Heromyth wrote:
 I want to get the UDAs for for a function parameter. Here the 
 test code and I got some errors:

 I think my blog aside is one of the few if only write-ups on 
 how to do this:

 http://dpldocs.info/this-week-in-d/Blog.Posted_2019_02_11.html#how-to-get-uda-on-a-function-param


 the library will not help much, you need to slice the 
 parameters yourself. (It might work combine lib stuff with 
 slice though, e.g. getUDA!(Parameters!F[1 .. 2]) maybe, i have 
 never tried).

 but this does work:

         static if(is(typeof(method) P == __parameters))
         foreach(idx, _; P) {{
 		// alias for convenience later
                 alias param = P[idx .. idx + 1]; // this slice 
 is the trick
 		// can get the identifier now
                 string ident = __traits(identifier, param);
 		// and the attributes
                 foreach(attr; __traits(getAttributes, param))
 			{}
 	}}

That's great! It should use
    static if(is(typeof(method) P == __parameters))
to get all the parameters instead of using:
    alias Params = Parameters!(member);


Here is the adjusted code:
=================================
import std.stdio;
import std.traits;
import std.meta;

struct Length {
     int a;
     int b;
}

class ClassA {
     void test( Length(1, 9) int len,  Length(2, 4) int size) {
         writeln("It's OK");
     }

     void test(string name,  Length(3, 5) int len) {
         writeln("Works now");
     }

     void test() {
     }
}

string test(T)() {
     string str;
     alias currentMembers = __traits(getOverloads, T, "test");

     static foreach(member; currentMembers) {{
         static if(is(typeof(member) Params == __parameters)) {
             static foreach(i, _; Params)
             {{
                 alias ThisParameter =  Params[i .. i + 1];
                 static foreach(uda; __traits(getAttributes, 
ThisParameter)) {
                     str ~= uda.stringof ~  "\n";
                 }
             }}
         }
     }}

     return str;
}

void main() {
     enum aa = test!(ClassA);
     writeln(aa);
}