string is rarely useful as a function argument

[Andrei Alexandrescu]

On 12/28/11 6:06 AM, Peter Alexander wrote:
> string is immutable(char)[]
>
> I rarely *ever* need an immutable string. What I usually need is
> const(char)[]. I'd say 99%+ of the time I need only a const string.
>
> This is quite irritating because "string" is the most convenient and
> intuitive thing to type. I often get into situations where I've written
> a function that takes a string, and then I can't call it because all I
> have is a char[]. I could copy the char[] into a new string, but that's
> expensive, and I'd rather I could just call the function.
>
> I think it's telling that most Phobos functions use 'const(char)[]' or
> 'in char[]' instead of 'string' for their arguments. The ones that use
> 'string' are usually using it unnecessarily and should be fixed to use
> const(char)[].
>
> In an ideal world I'd much prefer if string was an alias for
> const(char)[], but string literals were immutable(char)[]. It would
> require a little more effort when dealing with concurrency, but that's a
> price I would be willing to pay to make the string alias useful in
> function parameters.

I'm afraid you're wrong here. The current setup is very good, and much 
better than one in which "string" would be an alias for const(char)[].

The problem is escaping. A function that transitorily operates on a 
string indeed does not care about the origin of the string, but storing 
a string inside an object is a completely different deal. The setup

class Query
{
     string name;
     ...
}

is safe, minimizes data copying, and never causes surprises to anyone 
("I set the name of my query and a little later it's all messed up!").

So immutable(char)[] is the best choice for a correct string abstraction 
compared against both char[] and const(char)[]. In fact it's in a way 
good that const(char)[] takes longer to type, because it also carries 
larger liabilities.

If you want to create a string out of a char[] or const(char)[], use 
std.conv.to or the unsafe assumeUnique.


Andrei