== comparison of string literals, and their usage

[bauss]

On Saturday, 6 April 2019 at 19:47:14 UTC, lithium iodate wrote:
> On Saturday, 6 April 2019 at 15:35:22 UTC, diniz wrote:
>> So, I still could store and use and compare string pointers 
>> myself [1], and get valid results, meaning: pointer equality 
>> implies (literal) string equality. Or am I wrong? The point 
>> is, the parser, operating on an array of prescanned lexemes,  
>> will constantly check whether a valid lexeme is present simply 
>> by checking the lexeme "class". I don't want that to be a real 
>> string comp, too expesensive and for no gain.
>>
>> [1] As in the second comp of your example:
>> void main()
>> {
>>     auto c2 =  "one" == "two";
>>     auto c1 =  "one".ptr is "two".ptr;
>> }
>
> Not quite. D-strings strictly consist of pointer *and* length, 
> so you need to compare the .length properties as well to 
> correctly conclude that the strings equal. You can concisely do 
> that in one go by simply `is` comparing the array references as 
> in
>
> string a = "hello";
> string b = a;
> assert(a is b);
> assert(a[] is b[]);
>
> Of course, if the strings are never sliced, you can just 
> compare the pointers and be done, just make sure to document 
> how it operates. Depending on the circumstances I'd throw in 
> some asserts that do actual strings comparison to verify the 
> program logic.

To add onto this.

Here is an example why it's important to compare the length as 
well:

     string a = "hello";
     string b = a[0 .. 3];

     assert(a.ptr == b.ptr);
     assert(a.length != b.length);