Source file src/runtime/error.go

Documentation: runtime

  // Copyright 2010 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.
  
  package runtime
  
  import _ "unsafe" // for go:linkname
  
  // The Error interface identifies a run time error.
  type Error interface {
  	error
  
  	// RuntimeError is a no-op function but
  	// serves to distinguish types that are run time
  	// errors from ordinary errors: a type is a
  	// run time error if it has a RuntimeError method.
  	RuntimeError()
  }
  
  // A TypeAssertionError explains a failed type assertion.
  type TypeAssertionError struct {
  	interfaceString string
  	concreteString  string
  	assertedString  string
  	missingMethod   string // one method needed by Interface, missing from Concrete
  }
  
  func (*TypeAssertionError) RuntimeError() {}
  
  func (e *TypeAssertionError) Error() string {
  	inter := e.interfaceString
  	if inter == "" {
  		inter = "interface"
  	}
  	if e.concreteString == "" {
  		return "interface conversion: " + inter + " is nil, not " + e.assertedString
  	}
  	if e.missingMethod == "" {
  		return "interface conversion: " + inter + " is " + e.concreteString +
  			", not " + e.assertedString
  	}
  	return "interface conversion: " + e.concreteString + " is not " + e.assertedString +
  		": missing method " + e.missingMethod
  }
  
  // An errorString represents a runtime error described by a single string.
  type errorString string
  
  func (e errorString) RuntimeError() {}
  
  func (e errorString) Error() string {
  	return "runtime error: " + string(e)
  }
  
  // plainError represents a runtime error described a string without
  // the prefix "runtime error: " after invoking errorString.Error().
  // See Issue #14965.
  type plainError string
  
  func (e plainError) RuntimeError() {}
  
  func (e plainError) Error() string {
  	return string(e)
  }
  
  type stringer interface {
  	String() string
  }
  
  func typestring(x interface{}) string {
  	e := efaceOf(&x)
  	return e._type.string()
  }
  
  // For calling from C.
  // Prints an argument passed to panic.
  func printany(i interface{}) {
  	switch v := i.(type) {
  	case nil:
  		print("nil")
  	case stringer:
  		print(v.String())
  	case error:
  		print(v.Error())
  	case bool:
  		print(v)
  	case int:
  		print(v)
  	case int8:
  		print(v)
  	case int16:
  		print(v)
  	case int32:
  		print(v)
  	case int64:
  		print(v)
  	case uint:
  		print(v)
  	case uint8:
  		print(v)
  	case uint16:
  		print(v)
  	case uint32:
  		print(v)
  	case uint64:
  		print(v)
  	case uintptr:
  		print(v)
  	case float32:
  		print(v)
  	case float64:
  		print(v)
  	case complex64:
  		print(v)
  	case complex128:
  		print(v)
  	case string:
  		print(v)
  	default:
  		print("(", typestring(i), ") ", i)
  	}
  }
  
  // strings.IndexByte is implemented in runtime/asm_$goarch.s
  // but amusingly we need go:linkname to get access to it here in the runtime.
  //go:linkname stringsIndexByte strings.IndexByte
  func stringsIndexByte(s string, c byte) int
  
  // called from generated code
  func panicwrap() {
  	pc := make([]uintptr, 1)
  	n := Callers(2, pc)
  	if n == 0 {
  		throw("panicwrap: Callers failed")
  	}
  	frames := CallersFrames(pc)
  	frame, _ := frames.Next()
  	name := frame.Function
  	// name is something like "main.(*T).F".
  	// We want to extract pkg ("main"), typ ("T"), and meth ("F").
  	// Do it by finding the parens.
  	i := stringsIndexByte(name, '(')
  	if i < 0 {
  		throw("panicwrap: no ( in " + frame.Function)
  	}
  	pkg := name[:i-1]
  	if i+2 >= len(name) || name[i-1:i+2] != ".(*" {
  		throw("panicwrap: unexpected string after package name: " + frame.Function)
  	}
  	name = name[i+2:]
  	i = stringsIndexByte(name, ')')
  	if i < 0 {
  		throw("panicwrap: no ) in " + frame.Function)
  	}
  	if i+2 >= len(name) || name[i:i+2] != ")." {
  		throw("panicwrap: unexpected string after type name: " + frame.Function)
  	}
  	typ := name[:i]
  	meth := name[i+2:]
  	panic(plainError("value method " + pkg + "." + typ + "." + meth + " called using nil *" + typ + " pointer"))
  }
  

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