On 11/08/2013 05:47 PM, Igor Bukanov wrote:
C++'s `string` and `vector<T>` are objects containing two or three pointers.
For that one pays performance penalty in C++ as string and vector
instances are passed by references resulting in double indirection
when accessing the elements. I suppose it could help to think about
strings in Rust similar to variable-sized structs in C like:
struct MyString {
unsigned int bytelength;
unsigned int data[];
};
As in Rust such struct cannot be instantiated and one typically uses
malloc/alloca to allocate instances and then just pass around the
resulting pointers.
I like this version precisely for the reason it avoids double indirection. I use
it whenever I need "weighted strings" in C (strings that know their weight,
Pascal strings in fact) [1]. It works fine, is easy on the implementation side,
just terribly annoying w/o syntactic support. Same for arrays, both fixed (but
variable, in the sense of not predefined) and dynamic size.
It's all fine in my view for a language like Rust, provided it remains an
implementation choice. Meaning, whether the representation of say a static array
is a {p, n} struct or such a variable-sized structs is transparent on the
language side.
What are the present implementations of strings and arrays in Rust? And what
about fixed size (esp for strings)?
Denis
[1] Actually, I rather just use a pointer, with the size written before the
first string byte or array item, like true Pascal strings, but the result is the
same.
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