Withkeyword

Statement block to allow implicit access to fields in a user defined type variable

Syntax

With user_defined_var

statements

End With

Description

The With...End With block allows the omission of the name of a variable of a user-defined Type when referring to its fields. The fields may then be accessed with just a single period (.) before them, e.g. if the Type contains an field element called "element", then it could be accessed within the With block as ".element".

It can be used as a shorthand to save typing and avoid cluttering the source.
With can also be used with dereferenced pointers as the second example shows, with temporary instances (with explicit or implicit constructor) as the third example, and even with temporary types (without any constructor), because destruction of such temporary instances/types is deferred to the end of the With scope.
But returns byref of functions from temporary instances/types taken as arguments are not supported (and no error message).

With blocks may be nested. In this case, only the innermost With block is active, and any outer ones are ignored until the inner one is closed again. See the third example for an illustration of this.

Internally, the address of the variable is taken at the start of the With block, and then is used to calculate any element accesses within the block.
Note that this means that Goto should not be used to jump into a With block, otherwise the address will not have been set, and the results of trying to access it will be undefined.

Note for With block used inside member procedure:
To access duplicated symbols defined as global outside the Type, add two dots as prefix: "..SomeSymbol" (inside a With...End With block).

Remarks

Version

Before fbc 1.10.0, temporary types (without any constructor) were not supported (because destruction of such temporary types was called immediately after the With statement).

Dialect Differences

Not available in the -lang qb dialect unless referenced with the alias __With.
In the -lang qb and -lang fblite dialects, variables declared inside a With..End With block have a function-wide scope as in QB.
In the -lang fb and -lang deprecated dialects, variables declared inside a With..End With block are visible only inside the block, and can't be accessed outside it.

Differences from QB

New to FreeBASIC

Example

Type rect_type

    x As Single

    y As Single

End Type



Dim the_rectangle As rect_type

Dim As Integer temp, t



With the_rectangle

    temp = .x

    .x = 234 * t + 48 + .y

    .y = 321 * t + 2

End With

Type rect_type

    x As Single

    y As Single

End Type



Dim the_rectangle As rect_type Ptr



the_rectangle = CAllocate( 5 * Len( rect_type ) )



Dim As Integer loopvar, temp, t



For loopvar = 0 To 4



  With the_rectangle[loopvar]  '' dereferenced pointer



    temp = .x

    .x = 234 * t + 48 + .y

    .y = 321 * t + 2



  End With



Next

Type rect_type

    x As Single

    y As Single

    Declare Constructor()

    Declare Constructor(ByVal x0 As Single, ByVal y0 As Single)

End Type



Constructor rect_type()

End Constructor



Constructor rect_type(ByVal x0 As Single, ByVal y0 As Single)

    This.x = x0

    This.y = y0

End Constructor



Dim the_rectangle As rect_type



With rect_type(1, 2)  '' temporary instance created here held up to 'End With'

    the_rectangle.x = .x + .y  '' 1 + 2 = 3

    the_rectangle.y = .x - .y  '' 1 - 2 = -1

End With

Type rect_type

    x As Single

    y As Single

End Type



Dim As rect_type rect1, rect2



'' Nested With blocks

With rect1



    .x = 1

    .y = 2



    With rect2



        .x = 3

        .y = 4



    End With



End With



Print rect1.x, rect1.y '' 1,  2

Print rect2.x, rect2.y '' 3,  4

Reference

Documented in KeyPgWith.html