The limitations of constants in PHP

[chinmay.sahoo]

Class constants are fine as long as they’re willing to do our bidding, but their limitations tend to show up early. The value of a constant can be set only when it’s defined, and it cannot be defined inside methods in a class. You can only assign plain values to a constant; there is no way to assign an object to it. You can’t even use string concatenation when defining a constant.

 

[umesh11]

It is possible to define constant values on a per-class basis remaining the same and unchangeable. Constants differ from normal variables in that you don't use the $ symbol to declare or use them.
The value must be a constant expression, not (for example) a variable, a property, or a function call.

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