Re: try find the fastest way to convert a group string into index?

[Vladimir Panteleev via Digitalmars-d-learn]

On Sunday, 16 September 2018 at 10:04:09 UTC, learnfirst1 wrote:
how to make this more fast like with one loop and get the 
results.

This is a more general problem than any specific programming 
language; you may want to look into perfect hashing:

https://en.wikipedia.org/wiki/Perfect_hash_function

There exists software to generate perfect hash functions, e.g. 
GNU gperf:

https://www.gnu.org/software/gperf/

It looks like Basile wrote one for D:

https://github.com/BBasile/IsItThere

If you don't want to go that far, you can generate a string 
switch using string mixins:

void main()
{
        static immutable string[] keywords = ["foo", "bar", "baz"];
        enum Keyword { foo, bar, baz }

        Keyword parseKeyword(string s)
        {
                switch (s)
                {
                        mixin({
                                string code;
                                foreach (keyword; keywords)
					code ~= `case "` ~ keyword ~ `": return Keyword.` ~ keyword 
~ `;`;
                                return code;
                        }());
                        default:
                                throw new Exception("No such keyword!");
                }
        }
        assert(parseKeyword("bar") == Keyword.bar);
}