• d-bugmail puremagic.com (49/49) Nov 29 2013 https://d.puremagic.com/issues/show_bug.cgi?id=11642

d-bugmail puremagic.com writes:

https://d.puremagic.com/issues/show_bug.cgi?id=11642

           Summary: Handy object AA.setDefault function
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: bearophile_hugs eml.cc



I suggest to add to object.d another simple associative array function (similar
to get()), with the semantics of the Python "setdefault" dict method:

From the Python docs:

setdefault(key[, default]) 
If key is in the dictionary, return its value. If not, insert key with a value
of default and return default. default defaults to None.


A basic D implementation:


import std.traits;

TV1 setDefault(TK1, TV1, TK2, TV2)
              (ref TV1[TK1] aa, TK2 key, TV2 defVal=TV2.init)
if (is(Unqual!TK1 == Unqual!TK2) && is(Unqual!TV1 == Unqual!TV2)) {
    auto ptr = key in aa;
    if (ptr == null) {
        aa[key] = defVal;
        return defVal;
    } else
        return *ptr;
}

void main() {
    import std.stdio;

    char[int] aa;
    aa.setDefault(10, 'X').writeln;
    aa.writeln;
    aa.setDefault(20, 'Y').writeln;
    aa.writeln;
}


Output:

X
[10:'X']
Y
[20:'Y', 10:'X']


At first sight this small function could look a bit strange, but it turns out
to be quite handy to build associative arrays as you go inside an algorithm.

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