The D Scripting Language

[Per Ångström]

On 2010-11-15 14:27, spir wrote:
> On Mon, 15 Nov 2010 13:15:50 +0100
> Per Ångström<d-news at autark.se>  wrote:
>> string func(string s)
>> {
>>       /++
>>       // A handy feature of many scripting languages, but not in D
>>       // (in D, the type of the or-expression is bool):
>>       // The type of the or-expression is the type of the first
>>       // sub-expression that evaluates to true.
>>       return s || "default";
>>       +/
>>       // The D equivalent, arguably more readable but also more verbose:
>>       return s ? s : "default";
>> }
>
> More verbose?
> 	Real programmers *want* to type 3 more characters when this makes code clearer!
> ;-)

Verbosity is not only about more code to type, it's also about more code 
to read. My example was brief so of course that difference is 
negligible. Here's a somewhat more complex example which forces a 
trade-off between an extra temporary variable, evaluating the same 
expression twice or using a template:

/++
Simulates type-returning or-expression
+/
template or(T) {
     T _(T a, lazy T b) {T tmp = a; return tmp ? tmp : b;}
}

void m() {
     /+ least verbose, invalid D:
     string s = func("...") || "default";
     +/

     /+ valid D, but requires extra temp variable:
     string tmp = func("...");
     string s = tmp ? tmp : "default";
     +/

     /+ valid D, no temp variable but two (hopefully idempotent) 
function calls:
     string s = func("...") ? func(".,.") : "default";
     +/

     // valid D, but arguably ugly:
     string s = or!string._(func("..."), "default");
}
-- 
Per Å.