Select

The select instruction, selects one of its first two operands based on whether its third operand is zero or not. It shares some similarities with the ternary operator in other languages (e.g. false ? 10 : 20), but doesn't short-circuit. The instruction may be followed by an immediate value type: select (result T). select (result T) uses a different binary opcode, and allows types besides those introduced by the WebAssembly MVP (i32, i64, f32, f64), for example, it allows selection between two externref values.

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Syntax

wasm

;; push two values onto the stack
i32.const 10
i32.const 20

;; change to `1` (true) to get the first value (`10`)
i32.const 0
select

f32.const nan
f32.const -54.1

;; change to `1` (true) to get the first value (`nan`)
i32.const 0
select (result f32)

Instruction	Binary opcode
`select`	`0x1b`
`select t`	`0x1c`