lower case only first letter of word

[Steven Schveighoffer]

On 12/5/17 10:00 AM, Mengu wrote:
> On Tuesday, 5 December 2017 at 14:34:57 UTC, Mengu wrote:
>> On Tuesday, 5 December 2017 at 14:01:35 UTC, Marc wrote:
>>> On Tuesday, 5 December 2017 at 13:40:08 UTC, Daniel Kozak wrote:
>>>>>> [...]
>>>
>>> Yes, this is not what I want. I want to convert only the first letter 
>>> of the word to lower case and left all the others immutable. similar 
>>> to PHP's lcfirst():
>>>
>>> http://php.net/manual/en/function.lcfirst.php
>>
>> this is how i'd do it:
>>
>> string upcaseFirst(string wut) {
>>   import std.ascii : toUpper;
>>   import std.array : appender;
>>
>>   auto s = appender!string;
>>   s ~= wut[0].toUpper;
>>   s ~= wut[1..$];
>>   return s.data;
>> }
> 
> however a solution that does not allocate any memory would be a lot better.

Non-allocating version:

struct LowerCaseFirst(R) // if(isSomeString!R)
{
    R src;
    bool notFirst; // terrible name, but I want default false
    dchar front() {
       import std.uni: toLower;
       return notFirst ? src.front : src.front.toLower;
    }
    void popFront() { notFirst = true; src.popFront; }
    bool empty() { return src.empty; }
}

auto lowerCaseFirst(R)(R r)
{
    return LowerCaseFirst!R(r);
}

Warning: it ain't going to be fast. Auto-decoding everywhere.

-Steve