value.go

     1  // Copyright 2023 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 trace
     6  
     7  import (
     8  	"fmt"
     9  	"unsafe"
    10  )
    11  
    12  // Value is a dynamically-typed value obtained from a trace.
    13  type Value struct {
    14  	kind    ValueKind
    15  	pointer unsafe.Pointer
    16  	scalar  uint64
    17  }
    18  
    19  // ValueKind is the type of a dynamically-typed value from a trace.
    20  type ValueKind uint8
    21  
    22  const (
    23  	ValueBad ValueKind = iota
    24  	ValueUint64
    25  	ValueString
    26  )
    27  
    28  // Kind returns the ValueKind of the value.
    29  //
    30  // It represents the underlying structure of the value.
    31  //
    32  // New ValueKinds may be added in the future. Users of this type must be robust
    33  // to that possibility.
    34  func (v Value) Kind() ValueKind {
    35  	return v.kind
    36  }
    37  
    38  // ToUint64 returns the uint64 value for a ValueUint64.
    39  //
    40  // Panics if this Value's Kind is not ValueUint64.
    41  func (v Value) ToUint64() uint64 {
    42  	if v.kind != ValueUint64 {
    43  		panic("ToUint64 called on Value of a different Kind")
    44  	}
    45  	return v.scalar
    46  }
    47  
    48  // ToString returns the uint64 value for a ValueString.
    49  //
    50  // Panics if this Value's Kind is not ValueString.
    51  func (v Value) ToString() string {
    52  	if v.kind != ValueString {
    53  		panic("ToString called on Value of a different Kind")
    54  	}
    55  	return unsafe.String((*byte)(v.pointer), int(v.scalar))
    56  }
    57  
    58  func uint64Value(x uint64) Value {
    59  	return Value{kind: ValueUint64, scalar: x}
    60  }
    61  
    62  func stringValue(s string) Value {
    63  	return Value{kind: ValueString, scalar: uint64(len(s)), pointer: unsafe.Pointer(unsafe.StringData(s))}
    64  }
    65  
    66  // String returns the string representation of the value.
    67  func (v Value) String() string {
    68  	switch v.Kind() {
    69  	case ValueUint64:
    70  		return fmt.Sprintf("Value{Uint64(%d)}", v.ToUint64())
    71  	case ValueString:
    72  		return fmt.Sprintf("Value{String(%s)}", v.ToString())
    73  	}
    74  	return "Value{Bad}"
    75  }
    76
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