What cannot be used as a constant value in php

In PHP, expressions cannot be used as constant values ​​because they are not scalar types. The constant must be a valid identifier and its value must be an integer, float, string, or boolean.

What in PHP cannot be used as a constant value?

In PHP, what cannot be used as a constant value is an expression.

Constants are defined in PHP using the define() function, which requires providing a name and a value. The constant name must be a valid identifier and the value must be a scalar type (integer, float, string, or boolean).

Expressions cannot be used as constant values ​​because they are not scalar types. An expression can compute or operate on a value, but is not itself a value.

For example, the following declaration is invalid because it uses an expression (2 3) as a constant value:

<code class="php">define('MY_CONSTANT', 2 + 3);</code>

In contrast, the following declaration is valid because it A scalar value (5) is used as the constant value:

<code class="php">define('MY_CONSTANT', 5);</code>

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