eface and iface

src/runtime/runtime2.go

eface (empty interface)

  • empty interface 不包含方法的 interface 结构
  • data 是 nil，只要_type 不是 nil 这个 interface{} 就不是 nil
type eface struct {
    _type *_type
    data  unsafe.Pointer
}

// Needs to be in sync with ../cmd/link/internal/ld/decodesym.go:/^func.commonsize,
// ../cmd/compile/internal/gc/reflect.go:/^func.dcommontype and
// ../reflect/type.go:/^type.rtype.
// ../internal/reflectlite/type.go:/^type.rtype.
type _type struct {
    size       uintptr
    ptrdata    uintptr // size of memory prefix holding all pointers
    hash       uint32
    tflag      tflag
    align      uint8
    fieldAlign uint8
    kind       uint8
    // function for comparing objects of this type
    // (ptr to object A, ptr to object B) -> ==?
    equal func(unsafe.Pointer, unsafe.Pointer) bool
    // gcdata stores the GC type data for the garbage collector.
    // If the KindGCProg bit is set in kind, gcdata is a GC program.
    // Otherwise it is a ptrmask bitmap. See mbitmap.go for details.
    gcdata    *byte
    str       nameOff
    ptrToThis typeOff
}

iface (non-empty interface)

  • 方法的具体实现存放在 itag.fun 变量中
  • 如果 interface 包含多个方法
    • iface 里有个 hash table runtime/iface.go
  • inter *interfacetype 包含 interface 本身的信息，比如 package path、method。
type iface struct {
    tab  *itab
    data unsafe.Pointer
}

// layout of Itab known to compilers
// allocated in non-garbage-collected memory
// Needs to be in sync with
// ../cmd/compile/internal/gc/reflect.go:/^func.dumptabs.
type itab struct {
    inter *interfacetype
    _type *_type
    hash  uint32 // copy of _type.hash. Used for type switches.
    _     [4]byte
    fun   [1]uintptr // variable sized. fun[0]==0 means _type does not implement inter.
}

type imethod struct {
    name nameOff
    ityp typeOff
}

type interfacetype struct {
    typ     _type
    pkgpath name
    mhdr    []imethod
}

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