String interpolation would be pretty much just as bad for performance because it still requires the entire declaration to be put in a string, rather than just an identifier. That whole string needs to be formatted and turned into code, when we'd rather be reading code in the first place!

On Wednesday, 2 February 2022 at 12:24:32 UTC, Nick Treleaven wrote:

If you have to use a mixin for an identifier on a regular basis then that suggests to me that something is wrong with the design of the application or that some other language feature is missing.

mixin should be viewed as an emergency escape hatch compenstating for language deficiencies, not as a solution.

If you have to use a mixin for an identifier on a regular basis

much smaller scope. I do not buy any argument that it would encourage mixin strings. In metaprogramming you do what is necessary for best runtime performance.

On Saturday, 29 January 2022 at 21:24:09 UTC, mesni wrote:

static foreach(name; ["boo", "foo"]){
    string file_#name = readText(name~".txt");
    string file_#name#_info = readText(name~".meta");
    auto ##name = file_#name#_info.parseInfoFile;
}

writeln(file_boo);
writeln(boo);
writeln(file_foo_info);

I believe a DIP would be necessary, but to be honest I don't see a reason for this.

You can just do this which isn't really much less readable.

    static foreach (name; ["boo", "foo"])
    {
        mixin(`string file_%1$s = readText("%1$s.txt");`.format(name));
    }

    writeln(file_boo);
    writeln(file_foo);

And if D ever gets interpolated strings then the whole format can be removed and it could probably become something like this:

    static foreach (name; ["boo", "foo"])
    {
        mixin(i`string file_$name = readText("$name.txt");`);
    }

    writeln(file_boo);
    writeln(file_foo);

So personally I don't see a reason for your suggestion to be added.

I think it's just going to introduce more complexity than it's worth.

On Monday, 31 January 2022 at 07:19:49 UTC, bauss wrote:

static foreach(name; ["boo", "foo"]){
    string file_#name = readText(name~".txt");
    string file_#name#_info = readText(name~".meta");
    auto ##name = file_#name#_info.parseInfoFile;
}

writeln(file_boo);
writeln(boo);
writeln(file_foo_info);

    static foreach (name; ["boo", "foo"])
    {
        mixin(`string file_%1$s = readText("%1$s.txt");`.format(name));
    }

    writeln(file_boo);
    writeln(file_foo);

    static foreach (name; ["boo", "foo"])
    {
        mixin(i`string file_$name = readText("$name.txt");`);
    }

    writeln(file_boo);
    writeln(file_foo);

One big disadvantage interpolated strings have is you have to put the full declaration in a string. No big deal for a statement, but if the name of a function depends on compile-time stuff, the whole function is a string.

A much easier solution to this is allowing mixin() as an Identifier in general:

 Identifier:
     IdentifierStart
     IdentifierStart IdentifierChars
+    MixinExpression

So, you'd do

static foreach(name; ["boo", "foo"])
{
    enum string file_name_info = "file_" ~ name ~ "_info";
    string mixin("file_", name) = readText(name ~ ".txt");
    string mixin(file_name_info) = readText(name ~ ".meta");
    auto mixin(name) = mixin(file_name_info).parseInfoFile;
}

A much easier solution to this is allowing mixin() as an Identifier in general:

 Identifier:
     IdentifierStart
     IdentifierStart IdentifierChars
+    MixinExpression

So, you'd do

static foreach(name; ["boo", "foo"])
{
    enum string file_name_info = "file_" ~ name ~ "_info";
    string mixin("file_", name) = readText(name ~ ".txt");
    string mixin(file_name_info) = readText(name ~ ".meta");
    auto mixin(name) = mixin(file_name_info).parseInfoFile;
}

On Monday, 31 January 2022 at 07:19:49 UTC, bauss wrote:

    static foreach (name; ["boo", "foo"])
    {
        mixin(`string file_%1$s = readText("%1$s.txt");`.format(name));
    }

    writeln(file_boo);
    writeln(file_foo);

Using std.format for this incurs a substantial compile-time performance penalty--dozens of templates must be instantiated, memory must be allocated for CTFE, the format string must be validated, etc. If the mixin is inside a template which is itself instantiated many times, this overhead can really add up.