Enhancement: Raise minimum PHP version to PHP 7.1

[localheinz]

This PR

• raises the minimum PHP version from PHP 5.5 to PHP 7.1
• updates phpunit/phpunit
• ...

💁‍♂️ For reference, see http://tinyletter.com/mwopzend/letters/zend-framework-community-news-for-the-week-of-2017-04-20.

[froschdesign]

@localheinz
Develop branch!

[localheinz]

Ha, thank you, @froschdesign! Will take a look later!

[localheinz]

@froschdesign @weierophinney

What do you think, should we also use

• strict types
• scalar type hints
• return type declarations

?

[froschdesign]

@localheinz

• strict types
• scalar type hints
• return type declarations

• Void return types
• Nullable types
• "iterable" pseudo-type
• …

All features which simplify the code and make the interfaces more clear.

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Btw. HHVM makes no sense if we allow failures on Travis.

[weierophinney]

This is a great start. However, per your question:

What do you think, should we also use

strict types
scalar type hints
return type declarations

The answer is yes. Adopting PHP 7.1 as the new minimum version should really only happen if we are going to make use of those features, particularly as they affect consumers (extending classes or implementing interfaces means changes when we add these type hints).

I'll be merging #43 shortly, and issuing a new release when done. After that, rebase this based on the new status of develop, and let's see how far you can take it!