I'm trying to compile the onDispatch demo program from "The D Programming Language" (page 387). At first I had an import problem, but I fixed that. Now, however, when I try to call "a.do_something_cool", I get an error message saying:

onDispatch.d(43): Error: no property 'do_something_cool' for type 'onDispatch.A'

Full program follows (into onDispatch.d):
import core.stdc.ctype;
import std.stdio;

string underscoresToCamelCase(string sym) {
    string result;
    result.reserve(sym.length);
    bool makeUpper;
    foreach (c; sym) {
        if (c == '_') {
            makeUpper = true;
        } else {
            if (makeUpper) {
                result ~= toupper(c);
                makeUpper = false;
            } else {
                result ~= c;
            }
        }
    }
    return result;
}

unittest {
    assert(underscoresToCamelCase("hello_world") == "helloWorld");
    assert(underscoresToCamelCase("_a") == "A");
    assert(underscoresToCamelCase("abc") == "abc");
    assert(underscoresToCamelCase("a_bc_d_") == "aBcD");
}

class A {
    auto onDispatch(string m, Args...)(Args args) {
        // return mixin("this."~underscoresToCamelCase(m)~"(args)");
    }

    void doSomethingCool(int x, int y) {
        writeln("Do something cool");
    }
}

unittest {
    auto a = new A;
    a.doSomethingCool(5, 6);
    a.do_something_cool(5, 6);
}

On Thu, 21 Aug 2014 05:39:14 +0000
Shachar via Digitalmars-d-learn <digitalmars-d-learn@puremagic.com>
wrote:

> auto onDispatch(string m, Args...)(Args args)
first: opDispatch, not onDispatch.

second: underscoresToCamelCase() can't be evaluated in compile-time
anymore. the necessary changes:

1. add 'import std.string' -- we need toUpper() from this module.
2. change toupper(c) to toUpper(c) (first thing why ctfe fails)
3. remove 'result.reserve(sym.length);' line (second thing why ctfe
fails).
4. uncomment 'return' in opDispatch. %-)

that will do the trick.

to check if underscoresToCamelCase() can be evaluated in compile time, you can add this line to the first unittest block:

  enum t = underscoresToCamelCase("hello_world");

then compiler will tell you why it can't evaluate the function.

On Thu, 21 Aug 2014 05:39:14 +0000
Shachar via Digitalmars-d-learn <digitalmars-d-learn@puremagic.com>
wrote:

that's it: failing to evaluate opDispatch() template is not a
compilation error. compiler will silently try to find direct method if
opDispatch() fails. so be very careful with it.

you can add pragma(msg, "...") to your opDispatch to see if it really
compiles without errors. i.e.

  auto onDispatch(string m, Args...)(Args args) {
    pragma(msg, "m="~m);
    enum t = underscoresToCamelCase(t);
    pragma(msg, "t="~t);
    return mixin("this."~t~"(args)");
 }

you should see output of this pragmas in compile-time. if you can't see "t", for example, it means that evaluation of underscoresToCamelCase() failed.

On Thursday, 21 August 2014 at 06:11:06 UTC, ketmar via Digitalmars-d-learn wrote:
> that will do the trick.
>
Indeed. I ended up simply directly calling "a.opDispatch!"do_something_cool"(5, 6)", which brought most of those issues to light.

Shachar

On Thu, 21 Aug 2014 06:34:10 +0000
Shachar via Digitalmars-d-learn <digitalmars-d-learn@puremagic.com>
wrote:

> Indeed. I ended up simply directly calling "a.opDispatch!"do_something_cool"(5, 6)", which brought most of those issues to light.
ah, silly me. i forgot about such simple thing.