Question

I’ve noticed many (all?) PHP constants have a single-letter prefix, like E_NOTICE, T_STRING, etc. When defining a set of class constants that work in conjunction with one another, do you prefer to follow similar practice, or do you prefer to be more verbose?

class Foo {
    // let's say 'I' means "input" or some other relevant word
    const I_STRING = 'string';
    const I_INTEGER = 'integer';
    const I_FLOAT = 'float';
}

or

class Bar {
    const INPUT_STRING = 'string';
    const INPUT_INTEGER = 'integer';
    const INPUT_FLOAT = 'float';
}

Answer 1

Up until 5.3 PHP was limited to a single global namespace. Meaning any constants declared with define or built into the language required a prefix to partition themselves – namespacing on the cheap, if you will.

About constants themselves: while E_NOTICE is easier to type than ERROR_NOTICE the former has the major disadvantage of not being self-documenting. When in a global context not only do you need to partition constants out by prefix, these prefixes should also be as descriptive as possible.

Class constants are a slightly different beast, as you’ll always be referencing them by class name – partitioning will be built in. So you’ll end up with Account::STATUS_CONFIRMED and Account::STATUS_BANNED. But if I planned on having several dozen statuses, I’d put these in their own class, e.g. AccountStatus::CONFIRMED, AccountStatus::BANNED, etc.

Whatever naming convention you decide on for constants the major considerations are partitioning and self-documenting names (verbosity).