implement NSString.boolValue

[jpsim]

Gives same output as Standard Foundation for the same test values.

[phausler]

the value "+000009" should map to true

[harlanhaskins]

The NSString documentation says:

This property is YES on encountering one of "Y", "y", "T", "t", or a digit 1-9—the method ignores any trailing characters. This property is NO if the receiver doesn’t begin with a valid decimal text representation of a number.

The property assumes a decimal representation and skips whitespace at the beginning of the string. It also skips initial whitespace characters, or optional -/+ sign followed by zeroes.

It looks like, instead of checking the prefix for each character, it walks the string and checks if any of the characters match the predicates.
But it should also skip + or - and any number of 0's.

[jpsim]

Thanks for the tip @harlanhaskins! This one's on me, I should have referred to the documentation.

[jpsim]

I have an implementation in place, but I also had to implement NSScanner.rangeOfCharacterFromSet (...) which I'll package up in another PR.

[jpsim]

This has been updated to address @phausler's feedback and abide by the documentation referred to by @harlanhaskins. This depends on #75.

[harlanhaskins]

Looks great! 👍

[jpsim]

Now that #75 has been merged, I've dropped that commit from this branch, so now this just has the NSString.boolValue commit.

[parkera]

Thanks!