Type (Temporary)

• Source: https://www.freebasic.net/wiki/wikka.php?wakka=KeyPgTypeTemp
• Last revised: 2024-12-14

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Creates a temporary copy of a user defined type

Syntax

result = Type( initializers, ... )

or

result = Type<typename>( initializers, ... )

Parameters

initializers

Initial values for the type (or only the firsts)

typename

The name of the Type or Union

Return Value

A temporary copy of the type.

Description

Used to create a temporary type. If typename is not explicitly given, it will be inferred from its usage if possible. Usage of the temporary copy may include assigning it to a variable, passing it as a parameter to a procedure, or returning it as a value from a procedure.

For a type without own or inherited constructor (excluding also any type that is directly or indirectly derived from Object), the temporary type syntax is allowed if all type data-fields (including those inherited) are numeric primitives only and without any default initializers.

If at same time the type is without destructor, the compiler does a direct assignment instead of using a temporary copy.

The Constructor for the type, if there is one with parameters matching with the initializers provided, will be called when the temporary copy is created, and the Destructor for the type, if there is one, will be called immediately after its use. But when there is a matching constructor, the temporary type expression may be simply replaced by typename( initializers, ... ).

If there is a constructor at least but none which matches with the initializers, the temporary type syntax is obviously disallowed.

It can create not only a temporary copy of an user defined type, but also a temporary copy of predefined data-type as a variable-length string or any numeric data-type (all standard data-types excluding fixed-length strings).

It can also be used as an even shorter shortcut than With (see below) if you are changing all the data-fields (or the n firsts only).

A temporary object is destroyed at the end of execution of the statement (where it's defined), but its corresponding allocated memory is not released and remains available (unused) until going out the scope where statement is.

In the particular case where a temporary type is used in a With expression, the destruction of the temporary type is deferred to the end of the With scope.

Note: Static qualifier used at procedure definition level does not apply to temporary types.

Examples

start GeSHi

Type Example
    As Integer field1
    As Integer field2
End Type

Dim myexample As Example

'' Filling the type by setting each field
myexample.field1 = 1
myexample.field2 = 2

'' Filling the type by setting each field using WITH
With myexample
    .field1 = 1
    .field2 = 2
End With

'' Fill the variable's fields with a  temporary type
myexample = Type( 1, 2 )

end GeSHi

start GeSHi

'' Passing a user-defined types to a procedure using a temporary type
'' where the type can be inferred.

Type S
  As Single x, y
End Type

Sub test ( v As S )
  Print "S", v.x, v.y
End Sub

test( Type( 1, 2 ) )

end GeSHi

start GeSHi

'' Passing a user-defined type to a procedure using temporary types
'' where the type is ambiguous and the name of the type must be specified.

Type S
  As Single x, y
End Type

Type T
  As Integer x, y
End Type

Union U
  As Integer x, y
End Union

'' Overloaded procedure test()
Sub test Overload ( v As S )
  Print "S", v.x, v.y
End Sub

Sub test ( v As T )
  Print "T", v.x, v.y
End Sub

Sub test ( v As U )
  Print "U", v.x, v.y
End Sub

'' Won't work: ambiguous
'' test( type( 1, 2 ) )

'' Specify name of type instead
test( type<S>( 1, 2 ) )
test( type<T>( 1, 2 ) )
test( type<U>( 1 ) )

end GeSHi

Differences from QB

• New to FreeBASIC

See also

• Type...End Type
• Type (Alias)

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