Sizeof tip for Go types

Just a small tip to check yourself when organizing structs.

import . "unsafe"

Fixed sizes

Type	`Sizeof()` bytes
`struct{}`	0
`[0]Type`	0
`bool`	1
`int8`, `uint8`, `byte`	1
`int16`, `uint16`	2
`int32`, `uint32`, `rune`	4
`float32`	4
`int`, `uint`	4 or 8
`int64`, `uint64`	8
`float64`	8
`complex64`	8
`uintptr`	8
`struct{}`, `Type`	8
`map[Type1]Type2`	8
`chan Type`	8
`func()`	8
`string`	16
`complex128`	16
`[]Type`	24

Array

Formula: Sizeof([N]Type) = N * Sizeof(Type)

Examples:

Type	`Sizeof()` bytes
`[5]bool`	5
`[2][]bool{}`	48

Struct

Struct size depends on how struct is packed.

Formula:
Sizeof(struct{T1; ... TN}) = StructPackSize * PacksNum,
where StructPackSize = min(max(Sizeof(T1), ... Sizeof(TN)), Sizeof(uintptr))
and PacksNum depends on how struct fields are packed due to their order.

Examples:

Type	`StructPackSize`	`PacksNum`	`Sizeof()` bytes
`struct{a struct{}}`	0	1	0
`struct{a struct{}; b bool}`	1	1	1
`struct{b bool; u int32}`	4	2	8
`struct{a bool; b bool; u int32}`	4	2	8
`struct{u int32; a bool; b bool}`	4	2	8
`struct{a bool; u int32; b bool}`	4	3	12
`struct{a bool; s string; b bool}`	8	4	32

tyranron/go-sizeof-tip

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