Noissue - add SplitString and TrimSpaces helpers

- add `DependentString TrimSpaces(const String& value)` removing ASCII space characters on both sides of the argument
- add `std::pair<DependentString, DependentString> SplitString(const String& value, String::size_type separatorPos)` splitting the string into two parts without a separator character

Review: https://codereview.adblockplus.org/29712634

# It's extracted from https://codereview.adblockplus.org/29548581/

[hub, 2018-03-01 18:40:07]

https://codereview.adblockplus.org/29712634/diff/29712647/compiled/String.cpp
File compiled/String.cpp (right):

https://codereview.adblockplus.org/29712634/diff/29712647/compiled/String.cpp...
compiled/String.cpp:28: if (value[start] > u' ')
we could write this loop as `for (; start < end && value[start] <= u' ';
++start)`

Even though I'm not sure if the compiler would generate more efficient code.

https://codereview.adblockplus.org/29712634/diff/29712647/compiled/String.cpp...
compiled/String.cpp:45: };
what if secondBeginPos > value.length() ? since size_type is unsigned, it would
lead to undefined behaviour

[sergei, 2018-03-01 21:14:12]

https://codereview.adblockplus.org/29712634/diff/29712647/compiled/String.cpp
File compiled/String.cpp (right):

https://codereview.adblockplus.org/29712634/diff/29712647/compiled/String.cpp...
compiled/String.cpp:28: if (value[start] > u' ')
On 2018/03/01 18:40:07, hub wrote:
> we could write this loop as `for (; start < end && value[start] <= u' ';
> ++start)`
> 
> Even though I'm not sure if the compiler would generate more efficient code.

Yes, but I rather wanted to separate that comparison in order to improve the
readability (pretty subjective though) and because I thought that perhaps that
condition could be changed, so it will be easier to do it. If you want I can
change it of course.

https://codereview.adblockplus.org/29712634/diff/29712647/compiled/String.cpp...
compiled/String.cpp:45: };
On 2018/03/01 18:40:07, hub wrote:
> what if secondBeginPos > value.length() ? since size_type is unsigned, it
would
> lead to undefined behaviour

value.length(), secondBeginPos and len (the third arg of DependentString ctr)
are all unsigned integers which can represent the values, AFAIR (I googled,
https://stackoverflow.com/questions/28779803/is-subtracting-larger-unsigned-v...,
it's the same in C++14, the footnote is 48, though) the result of len should be
defined.

[hub, 2018-03-01 22:15:44]

LGTM

https://codereview.adblockplus.org/29712634/diff/29712647/compiled/String.cpp
File compiled/String.cpp (right):

https://codereview.adblockplus.org/29712634/diff/29712647/compiled/String.cpp...
compiled/String.cpp:28: if (value[start] > u' ')
On 2018/03/01 21:14:12, sergei wrote:
> On 2018/03/01 18:40:07, hub wrote:
> > we could write this loop as `for (; start < end && value[start] <= u' ';
> > ++start)`
> > 
> > Even though I'm not sure if the compiler would generate more efficient code.
> 
> Yes, but I rather wanted to separate that comparison in order to improve the
> readability (pretty subjective though) and because I thought that perhaps that
> condition could be changed, so it will be easier to do it. If you want I can
> change it of course.

Acknowledged.

https://codereview.adblockplus.org/29712634/diff/29712647/compiled/String.cpp...
compiled/String.cpp:45: };
On 2018/03/01 21:14:12, sergei wrote:
> On 2018/03/01 18:40:07, hub wrote:
> > what if secondBeginPos > value.length() ? since size_type is unsigned, it
> would
> > lead to undefined behaviour
> 
> value.length(), secondBeginPos and len (the third arg of DependentString ctr)
> are all unsigned integers which can represent the values, AFAIR (I googled,
>
https://stackoverflow.com/questions/28779803/is-subtracting-larger-unsigned-v...,
> it's the same in C++14, the footnote is 48, though) the result of len should
be
> defined.

Acknowledged.