Constant Expression

For the initialization expressions of globals, tables, offsets and element segments, they must be constant.

To be a constant expression, it must only contain the following instructions:

• *.const
• global.get
• ref.null
• ref.i31
• ref.func
• struct.new
• struct.new_default
• array.new
• array.new_default
• array.new_fixed
• any.convert_extern
• extern.convert_any

Constant expression example:

(module
  (global i32
    i32.const 2))

Non-constant expression example:

(module
  (global i32
    i32.const 1
    i32.const 2
    i32.add))