OPERATOR

• 来源: https://www.freebasic.net/wiki/wikka.php?wakka=KeyPgOperator
• 最后更新: 2021-11-18

---

声明或定义重载运算符。

语法

{ Type | Class | Union } typename

declare Operator cast () [ byref ] as datatype
declare Operator @ () [ byref ] as datatype ptr
declare Operator assignment_op ( [ byref | byval ] rhs as datatype )
declare Operator [] ( index as datatype ) [ byref ] as datatype
declare Operator new ( size as uinteger ) as any ptr
declare Operator new[] ( size as uinteger ) as any ptr
declare Operator delete ( buf as any ptr )
declare Operator delete[] ( buf as any ptr )

End { Type | Class | Union }

{ Type | Class | Union } typename

declare Operator For ()
declare Operator For ( [ byref | byval ] stp as typename )
declare Operator Step ()
declare Operator Step ( [ byref | byval ] stp as typename )
declare Operator Next ( [ byref | byval ] cond as typename ) as Integer
declare Operator Next ( [ byref | byval ] cond as typename, [ byref | byval ] stp as typename ) as Integer

End { Type | Class | Union }

declare Operator unary_op ( [ byref | byval ] rhs as datatype ) as datatype
declare Operator binary_op ( [ byref | byval ] lhs as datatype, [ byref | byval ] rhs as datatype ) as datatype

Operator typename.cast () [ byref ] as datatype [ Export ]
Operator typename.@ () [ byref ] as datatype ptr [ Export ]
Operator typename.assignment_op ( [ byref | byval ] rhs as datatype ) [ Export ]
Operator typename.[] ( index as datatype ) [ byref ] as datatype [ Export ]
Operator unary_op ( [ byref | byval ] rhs as datatype ) as datatype [ Export ]
Operator binary_op ( [ byref | byval ] lhs as datatype, [ byref | byval ] rhs as datatype ) as datatype [ Export ]
Operator typename.new ( size as uinteger ) as any ptr [ Export ]
Operator typename.new[] ( size as uinteger ) as any ptr [ Export ]
Operator typename.delete ( buf as any ptr ) [ Export ]
Operator typename.delete[] ( buf as any ptr ) [ Export ]

参数

typename

Type、Class、Union 或 Enum 的名称。

assignment_op

let += -= *= &= /= \= mod= shl= shr= and= or= xor= imp= eqv= ^=

unary_op

- not * -> abs sgn fix frac int exp log sin asin cos acos tan atn len sqr

binary_op

+ - * & / \ mod shl shr and or xor imp eqv ^ = <> < > <= >=

描述

内置运算符（如 =、+ 和 cast）在表达式中使用时具有预定义的行为。当运算符的至少一个参数是 Type、Class、Enum 或 Union 数据类型时，可以对这些运算符进行重载，使其执行预定义操作以外的功能。

运算符本质上就是函数。运算符 + 的功能类似于 Function Plus( A as DataType, B as DataType ) as DataType。更多信息请参见 运算符重载。运算符可以被重载以接受不同的数据类型作为参数。Cast 运算符是唯一一种可以在仅返回类型不同时多次声明的运算符（或函数），但返回类型不能与其所在的 Type、Class 或 Union 相同（对于非显式用法，编译器可能根据对象的使用方式决定调用哪个 cast 重载）。

非静态运算符成员在 Type、Class 或 Union 内部声明。全局运算符在外部声明。所有运算符定义（过程体）必须出现在外部。

Let、Cast 和其他赋值运算符必须在 Type、Class 或 Union 内部声明。与所有非静态成员过程一样，它们传递一个隐藏的 this 参数。

一元运算符必须在 Type、Class 或 Union 外部声明，并显式声明返回数据类型。一元运算符可以被重载以返回任何有效的数据类型，但 Operator -> (成员访问指针) 除外，它必须返回 Type、Class 或 Union 数据类型。

二元运算符必须在 Type、Class 或 Union 外部声明，并显式声明返回数据类型。二元运算符可以用有效的数据类型进行重载，包括关系运算符，它们也可以返回任何有效的数据类型。

Let 指赋值运算符，如 LET a=b。Let 关键字在实际使用中通常省略，在 -lang fb 方言中不允许使用。但是，Let() 可以用于将 UDT 的字段赋值给多个变量。

有关为用户定义类型重载 For..Next 语句的更多信息，请参见 For、Step 和 Next。

虽然在 Type、Class 或 Union 内部声明，但成员运算符 New、New[]、Delete 和 Delete[] 始终是静态的，即使未显式声明（static 关键字不必要，但允许使用）。

示例

start GeSHi

'' operator1.bas

Type Vector2D
  As Single x, y

  '' 返回包含向量数据的字符串。
  Declare Operator Cast() As String

  '' 将向量乘以一个标量。
  Declare Operator *= ( ByVal rhs As Single )
End Type

'' 允许两个向量相加。
Declare Operator + ( ByRef lhs As Vector2D, ByRef rhs As Vector2D ) As Vector2D

'' 使用重载的 abs() 运算符返回向量的模（单精度浮点数）。
Declare Operator Abs (  ByRef rhs As Vector2D ) As Single

Operator Vector2D.Cast () As String
  Return "(" + Str(x) + ", " + Str(y) + ")"
End Operator

Operator Vector2D.*= ( ByVal rhs As Single )
  This.x *= rhs
  This.y *= rhs
End Operator

Operator + ( ByRef lhs As Vector2D, ByRef rhs As Vector2D ) As Vector2D
  Return type<Vector2D>( lhs.x + rhs.x, lhs.y + rhs.y )
End Operator

Operator Abs ( ByRef rhs As Vector2D ) As Single
  Return Sqr( rhs.x * rhs.x + rhs.y * rhs.y )
End Operator

Dim a As Vector2D = type<Vector2D>( 1.2, 3.4 )
Dim b As Vector2D = type<Vector2D>( 8.9, 6.7 )
Dim c As Vector2D = type<Vector2D>( 4.3, 5.6 )

Print "a = "; a, "abs(a) ="; Abs( a )
Print "b = "; b, "abs(b) ="; Abs( b )
Print "a + b = "; a + b, "abs(a+b) ="; Abs( a + b )
Print "c = "; c, "abs(c) ="; Abs( c )
Print "'c *= 3'"
c *= 3
Print "c = "; c, "abs(c) ="; Abs( c )

end GeSHi

运算符 [] 的一个小用例：用于字节缓冲区的最简单智能指针。

start GeSHi

'' operator3.bas

'' 智能指针是一个行为类似指针但功能更多的对象：
'' - 该对象像指针一样灵活，同时具有对象的优势，
''   例如构造函数和析构函数会自动调用。
'' - 因此，当该对象超出作用域时，智能指针的析构函数将自动调用，
''   并删除用户指针。

'' 用于字节缓冲区的最简单智能指针示例：
'' - 构造函数和析构函数允许分配、释放和调整字节缓冲区大小。
'' - 指针索引运算符允许访问缓冲区元素。
'' - 复制构造函数和 let 运算符仅在私有区域声明，
''   以禁止复制构造和任何赋值操作。

Type smartByteBuffer
  Public:
    Declare Constructor (ByVal size As UInteger = 0)
    Declare Operator [] (ByVal index As UInteger) ByRef As Byte
    Declare Destructor ()
  Private:
    Declare Constructor (ByRef rhs As smartByteBuffer)
    Declare Operator Let (ByRef rhs As smartByteBuffer)
    Dim As Byte Ptr psbb
End Type

Constructor smartByteBuffer (ByVal size As UInteger = 0)
  This.Destructor()
  If size > 0 Then
    This.psbb = New Byte[size]
    Print "Byte buffer allocated"
  End If
End Constructor

Operator smartByteBuffer.[] (ByVal index As UInteger) ByRef As Byte
  Return This.psbb[index]
End Operator

Destructor smartByteBuffer ()
  If This.psbb > 0 Then
    Delete[] This.psbb
    This.psbb = 0
    Print "Byte buffer deallocated"
  End If
End Destructor

Scope
  Dim As smartByteBuffer sbb = smartByteBuffer(256)
  For I As Integer = 0 To 255
    sbb[I] = I - 128
  Next I
  Print
  For I As Integer = 0 To 255
    Print Using "#####"; sbb[I];
  Next I
  Print
End Scope

end GeSHi

方言差异

• 仅在 -lang fb 方言中可用。

参见

• Class
• Union
• Type
• 强制类型转换与转换

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