src/pkg/runtime/type.go

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

/*
 * Runtime type representation.
 *
 * The following files know the exact layout of these
 * data structures and must be kept in sync with this file:
 *
 *	../../cmd/gc/reflect.c
 *	../reflect/type.go
 *	type.h
 */

package runtime

import "unsafe"

// The compiler can only construct empty interface values at
// compile time; non-empty interface values get created
// during initialization.  Type is an empty interface
// so that the compiler can lay out references as data.
type Type interface{}

// All types begin with a few common fields needed for
// the interface runtime.
type commonType struct {
	size          uintptr // size in bytes
	hash          uint32  // hash of type; avoids computation in hash tables
	alg           uint8   // algorithm for copy+hash+cmp (../runtime/runtime.h:/AMEM)
	align         uint8   // alignment of variable with this type
	fieldAlign    uint8   // alignment of struct field with this type
	kind          uint8   // enumeration for C
	string        *string // string form; unnecessary  but undeniably useful
	*uncommonType         // (relatively) uncommon fields
}

// Values for commonType.kind.
const (
	kindBool = 1 + iota
	kindInt
	kindInt8
	kindInt16
	kindInt32
	kindInt64
	kindUint
	kindUint8
	kindUint16
	kindUint32
	kindUint64
	kindUintptr
	kindFloat
	kindFloat32
	kindFloat64
	kindArray
	kindChan
	kindFunc
	kindInterface
	kindMap
	kindPtr
	kindSlice
	kindString
	kindStruct
	kindUnsafePointer

	kindNoPointers = 1 << 7 // OR'ed into kind
)

// Method on non-interface type
type method struct {
	name    *string        // name of method
	pkgPath *string        // nil for exported Names; otherwise import path
	mtyp    *Type          // method type (without receiver)
	typ     *Type          // .(*FuncType) underneath (with receiver)
	ifn     unsafe.Pointer // fn used in interface call (one-word receiver)
	tfn     unsafe.Pointer // fn used for normal method call
}

// uncommonType is present only for types with names or methods
// (if T is a named type, the uncommonTypes for T and *T have methods).
// Using a pointer to this struct reduces the overall size required
// to describe an unnamed type with no methods.
type uncommonType struct {
	name    *string  // name of type
	pkgPath *string  // import path; nil for built-in types like int, string
	methods []method // methods associated with type
}

// BoolType represents a boolean type.
type BoolType commonType

// Float32Type represents a float32 type.
type Float32Type commonType

// Float64Type represents a float64 type.
type Float64Type commonType

// FloatType represents a float type.
type FloatType commonType

// Complex64Type represents a complex64 type.
type Complex64Type commonType

// Complex128Type represents a complex128 type.
type Complex128Type commonType

// ComplexType represents a complex type.
type ComplexType commonType

// Int16Type represents an int16 type.
type Int16Type commonType

// Int32Type represents an int32 type.
type Int32Type commonType

// Int64Type represents an int64 type.
type Int64Type commonType

// Int8Type represents an int8 type.
type Int8Type commonType

// IntType represents an int type.
type IntType commonType

// Uint16Type represents a uint16 type.
type Uint16Type commonType

// Uint32Type represents a uint32 type.
type Uint32Type commonType

// Uint64Type represents a uint64 type.
type Uint64Type commonType

// Uint8Type represents a uint8 type.
type Uint8Type commonType

// UintType represents a uint type.
type UintType commonType

// StringType represents a string type.
type StringType commonType

// UintptrType represents a uintptr type.
type UintptrType commonType

// UnsafePointerType represents an unsafe.Pointer type.
type UnsafePointerType commonType

// ArrayType represents a fixed array type.
type ArrayType struct {
	commonType
	elem *Type // array element type
	len  uintptr
}

// SliceType represents a slice type.
type SliceType struct {
	commonType
	elem *Type // slice element type
}

// ChanDir represents a channel type's direction.
type ChanDir int

const (
	RecvDir ChanDir             = 1 << iota // <-chan
	SendDir                                 // chan<-
	BothDir = RecvDir | SendDir             // chan
)

// ChanType represents a channel type.
type ChanType struct {
	commonType
	elem *Type   // channel element type
	dir  uintptr // channel direction (ChanDir)
}

// FuncType represents a function type.
type FuncType struct {
	commonType
	dotdotdot bool    // last input parameter is ...
	in        []*Type // input parameter types
	out       []*Type // output parameter types
}

// Method on interface type
type imethod struct {
	name    *string // name of method
	pkgPath *string // nil for exported Names; otherwise import path
	typ     *Type   // .(*FuncType) underneath
}

// InterfaceType represents an interface type.
type InterfaceType struct {
	commonType
	methods []imethod // sorted by hash
}

// MapType represents a map type.
type MapType struct {
	commonType
	key  *Type // map key type
	elem *Type // map element (value) type
}

// PtrType represents a pointer type.
type PtrType struct {
	commonType
	elem *Type // pointer element (pointed at) type
}

// Struct field
type structField struct {
	name    *string // nil for embedded fields
	pkgPath *string // nil for exported Names; otherwise import path
	typ     *Type   // type of field
	tag     *string // nil if no tag
	offset  uintptr // byte offset of field within struct
}

// StructType represents a struct type.
type StructType struct {
	commonType
	fields []structField // sorted by offset
}

/*
 * Must match iface.c:/Itab and compilers.
 */
type Itable struct {
	Itype  *Type // (*tab.inter).(*InterfaceType) is the interface type
	Type   *Type
	link   *Itable
	bad    int32
	unused int32
	Fn     [100000]uintptr // bigger than we'll ever see
}