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Source file src/runtime/error.go

     1	// Copyright 2010 The Go Authors. All rights reserved.
     2	// Use of this source code is governed by a BSD-style
     3	// license that can be found in the LICENSE file.
     4	
     5	package runtime
     6	
     7	// The Error interface identifies a run time error.
     8	type Error interface {
     9		error
    10	
    11		// RuntimeError is a no-op function but
    12		// serves to distinguish types that are run time
    13		// errors from ordinary errors: a type is a
    14		// run time error if it has a RuntimeError method.
    15		RuntimeError()
    16	}
    17	
    18	// A TypeAssertionError explains a failed type assertion.
    19	type TypeAssertionError struct {
    20		interfaceString string
    21		concreteString  string
    22		assertedString  string
    23		missingMethod   string // one method needed by Interface, missing from Concrete
    24	}
    25	
    26	func (*TypeAssertionError) RuntimeError() {}
    27	
    28	func (e *TypeAssertionError) Error() string {
    29		inter := e.interfaceString
    30		if inter == "" {
    31			inter = "interface"
    32		}
    33		if e.concreteString == "" {
    34			return "interface conversion: " + inter + " is nil, not " + e.assertedString
    35		}
    36		if e.missingMethod == "" {
    37			return "interface conversion: " + inter + " is " + e.concreteString +
    38				", not " + e.assertedString
    39		}
    40		return "interface conversion: " + e.concreteString + " is not " + e.assertedString +
    41			": missing method " + e.missingMethod
    42	}
    43	
    44	// An errorString represents a runtime error described by a single string.
    45	type errorString string
    46	
    47	func (e errorString) RuntimeError() {}
    48	
    49	func (e errorString) Error() string {
    50		return "runtime error: " + string(e)
    51	}
    52	
    53	// plainError represents a runtime error described a string without
    54	// the prefix "runtime error: " after invoking errorString.Error().
    55	// See Issue #14965.
    56	type plainError string
    57	
    58	func (e plainError) RuntimeError() {}
    59	
    60	func (e plainError) Error() string {
    61		return string(e)
    62	}
    63	
    64	type stringer interface {
    65		String() string
    66	}
    67	
    68	func typestring(x interface{}) string {
    69		e := efaceOf(&x)
    70		return e._type.string()
    71	}
    72	
    73	// For calling from C.
    74	// Prints an argument passed to panic.
    75	// There's room for arbitrary complexity here, but we keep it
    76	// simple and handle just a few important cases: int, string, and Stringer.
    77	func printany(i interface{}) {
    78		switch v := i.(type) {
    79		case nil:
    80			print("nil")
    81		case stringer:
    82			print(v.String())
    83		case error:
    84			print(v.Error())
    85		case int:
    86			print(v)
    87		case string:
    88			print(v)
    89		default:
    90			print("(", typestring(i), ") ", i)
    91		}
    92	}
    93	
    94	// called from generated code
    95	func panicwrap(pkg, typ, meth string) {
    96		panic(plainError("value method " + pkg + "." + typ + "." + meth + " called using nil *" + typ + " pointer"))
    97	}
    98	

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