Checking $mixed parameter type for PHP methods

Something that we came across this morning, and something to be wary of in the future, is how you check the parameter type of a $mixed variable in a method signature.

i.e. Is the parameter a string or a number?

If you’re not careful you can get unexpected results…

As we’ve discovered, using ctype functions can be dangerous as ctype_digit() for example expects a string as a parameter, so if you pass it an integer it will convert it to the ASCII equivalent, thus:

ctype_digit(65) = false

Because it’s basically doing:

ctype_digit('A') = false

And A isn’t a number. The exact opposite problem exists with ctype_alpha

ctype_alpha(65) = true

Because again it’s basically doing:

ctype_alpha('A') = true

One way to get around this, although of course you must be careful too, is to use is_numeric() to determine whether a variable is a number or not. Do not use is_string() or is_integer() as they have exactly the same problems as above, in that:

is_integer("65") = false
is_string("65") = true


is_numeric("65") = true
is_numeric(65) = true

However as has been mentioned to me since I wrote this, is that you have to be careful when handling floating point numbers, as if they end up being represented with a mantissa and exponent you can run into similar types of problems…

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