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Project: Array Utilities Unit
Unit: DelphiDabbler.Lib.ArrayUtils
Record: TArrayUtils
Applies to: ~>0.1
type
TCallback<T> = reference to procedure (const AElem: T);
class procedure ShiftAndRelease<T>(var A: TArray<T>;
const AReleaser: TCallback<T>);
static;
Deletes the first element of a non-empty array and releases any resources associated with the deleted element.
The length of the array is reduced by one.
Parameters:
A - Array from which the element is to be removed and its associated resource released. The array is updated in place.
AReleaser - Procedure called for the deleted element that must release any resource associated with the element.
Parameter(s):
Preconditions:
If it is not necessary release a resource associated with an element that is shifted off an array then Shift<T> should be used instead of ShiftAndRelease<T>.
There is no corresponding version of UnShift<T> for use with ShiftAndRelease<T>. This is not necessary since un-shifting an element with an associated resource requires no special handling. Just use UnShift<T>.
The example below use a custom TMockResource record that emulates a resource that must be released. The record keeps track of the number of records currently instantiated.
type
TMockResource = record
public
constructor Create(const AField: Integer);
procedure Release;
var Field: Integer;
class var InstanceCount: Cardinal;
end;
{ TMockResource }
constructor TMockResource.Create(const AField: Integer);
begin
Field := AField;
Inc(InstanceCount);
end;
procedure TMockResource.Release;
begin
Dec(InstanceCount);
end;
procedure ShiftAndRelease_Eg;
var
R, R0, R1, R2: TMockResource;
RA, Expected: TArray<TMockResource>;
begin
// create array of 3 "resources"
R0 := TMockResource.Create(0);
R1 := TMockResource.Create(1);
R2 := TMockResource.Create(2);
RA := TArray<TMockResource>.Create(R0, R1, R2);
Assert(Length(RA) = 3, '3 element array expected');
Assert(TMockResource.InstanceCount = 3, 'Expected 3 "resources" allocated');
Assert(TArrayUtils.First<TMockResource>(RA).Field = 0, '0 1st elem expected');
// pop and release element at end of array
TArrayUtils.ShiftAndRelease<TMockResource>(
RA,
procedure (const AElem: TMockResource) begin AElem.Release end
);
// check array after popping
Assert(TArrayUtils.First<TMockResource>(RA).Field = 1, '1 1st elem expected');
Assert(Length(RA) = 2, '2 element array expected following deletion');
Assert(TMockResource.InstanceCount = 2, 'Expected 2 "resources" allocated');
Expected := TArray<TMockResource>.Create(R1, R2);
Assert(TArrayUtils.Equal<TMockResource>(Expected, RA),
'updated array content not as expected');
// clear up remaining allocations
for R in RA do R.Release;
Assert(TMockResource.InstanceCount = 0, 'Expected all "resources" released');
end;