PHP define vs const

Question

In PHP, there are two ways to declare constants :

1. With define keyword

   define('FOO', 1);
   

2. Using const keyword

   const FOO = 1;
   

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• What are the main differences between those two?
• When and why should you use one and then use the other?

Answer 1

Const creates constants at compile-time, whereas define defines them at run time, which is the key distinction between the two methods. The majority of const's drawbacks stem from this.

Some disadvantages of const are:

•  Cannot be used to conditionally define constants. 
• Unlike define(), which accepts any expression, const accepts a static scalar (an integer, string, or other constant like true, false, null, or __FILE__). Constant expressions are now permitted in const since PHP 5.6.
• Unlike define(), which accepts any expression as a name, const requires a simple constant name.

I hope this helps you.