Re: How do I set a class member value by its name in a string?

[Biotronic via Digitalmars-d-learn]

On Wednesday, 27 December 2017 at 21:42:53 UTC, Mengu wrote:
On Wednesday, 27 December 2017 at 21:39:49 UTC, Mengu wrote:
On Wednesday, 27 December 2017 at 20:54:17 UTC, bitwise wrote:
[...]

there's also a simple workaround for fields with the same 
type: https://run.dlang.io/is/dsFajq

import std.stdio;

struct S {
  int x;
  int y;
}

auto setValue(ref S s, string field, int value) {
  foreach (fieldName; __traits(allMembers, S)) {
    if (fieldName == field) {
      __traits(getMember, s, fieldName) = value;
      break;
    }
  }
}

void main() {
  S s;
  s.setValue("x", 5);
  s.setValue("y", 25);
  writeln(s);
}


you can play with it to make it more generic. you can also 
create a mixin template that would generate setters for each 
field you would need a setter for and then in the run time 
you'd just be able to call them.

return type should just be void. that's just my muscle memory. 
:-D

More generic, for more better:

void setValue(T, V)(auto ref T aggregate, string field, V value)
{
    import std.traits : FieldNameTuple;
    import std.meta : Alias;
    switch (field)
    {
        foreach (fieldName; FieldNameTuple!T)
        {
            case fieldName:
                static if (is(typeof(__traits(getMember, 
aggregate, fieldName) = value)))
                {
                    __traits(getMember, aggregate, fieldName) = 
value;
                    return;
                }
                else assert(false, T.stringof ~ "."~field~" 
cannot be assigned from a "~V.stringof~".");
        }
        default:
            assert(false, T.stringof ~ " has no field named 
"~field~".");
    }
}

unittest {
    import std.exception : assertThrown;
    import core.exception : AssertError;

    static struct S {
        int x;
        string s;
    }

    S s;
    s.setValue("x", 14);
    assert(s.x == 14);
    assertThrown!AssertError(s.setValue("q", 14));
    assertThrown!AssertError(s.setValue("s", 14));
    s.setValue("s", "abc123");
    assert(s.s == "abc123");
}

unittest {
    import std.exception : assertThrown;
    import core.exception : AssertError;

    static class C {
        int x;
        string s;
    }

    C c = new C;
    c.setValue("x", 14);
    assert(c.x == 14);
    assertThrown!AssertError(c.setValue("q", 14));
    assertThrown!AssertError(c.setValue("s", 14));
    c.setValue("s", "abc123");
    assert(c.s == "abc123");

    (new C).setValue("x", 143);
}

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