I inherited a codebase that is filled with conditionals using terms like (isset($a) && !empty($a)) but the $a are actually long variable names and it's an eye-sore. I wanted to replace the expressions with $a??false but I wasn't sure if there was some case that wouldn't be the same.

Are these statements identical or is there some value of $a that would be different?

CodePudding user response：

Firstly, let's understand what the different elements are doing:

• isset takes a variable, array element, etc, and returns true if it exists, and has any value other than null
• empty takes a variable, array element, etc, and returns false if it exists, and has any value which would be considered equivalent to true
• ?? examines a variable, array element, etc, and returns its value if it exists, and has any value other than null; otherwise, it returns its right-hand argument
• any expression used in an if statement is cast to boolean automatically

So, we can look at the equivalences:

• empty is a combination of isset() and a cast to false; specifically, empty($a) === !isset($a) || !(bool)$a, so !empty($a) === isset($a) && (bool)$a
• ?? uses the same check as isset, not the same check as empty; so $a ?? false on its own is equivalent to isset($a) ? $a : false
• but, in an if statement, the whole thing will be forced to boolean, so if ( $a ?? false ) ... is equivalent to if ( (bool)(isset($a) ? $a : false) ) ... or more readably if ( isset($a) ? (bool)$a : false ) ...

Which brings us to the answer, which is that the following all do the same thing:

if ( isset($a) && !empty($a) ) ...
if ( isset($a) && !(bool)$a ) ... // empty() is just a bool cast   isset
if ( !empty($a) ) ... // the isset is actually redundant
if ( isset($a) ? (bool)$a : false ) ... // same logic as the && version
if ( (bool)($a ?? false) ) ... // ?? does the isset for us
if ( $a ?? false ) ... // if does the (bool) for us

Probably the most readable is just to use !empty($a) on its own, and leave ?? for where you actually need the original value rather than a true.