Declaration Rules — Where to Declare Each Type

Where each MtxVec type may be declared:

Declaration context	Value types (Vector, Matrix, VectorInt, MatrixInt)	Class types (TVec, TMtx, TVecInt, TMtxInt)
Local variable	YES (primary use)	YES — with CreateIt/FreeIt
Class/record field	NO — never	YES — with constructor/destructor

Rule 1: Value types must only be local variables. Never use them as fields.

Rule 2: Class types as fields — use constructor + destructor (not CreateIt/FreeIt):

TSomething = class
    FData: TVec;
    constructor Create;
    destructor Destroy; override;
end;
constructor TSomething.Create;
begin FData := TVec.Create; end;
destructor TSomething.Destroy;
begin FData.Free; inherited; end;

Rule 3: CreateIt / FreeIt are for local objects only — never for fields.

StringList — value type for string lists (unit: StringVar)

StringList is a value-type record wrapper around TStringList. It has the same API as TStringList (Add, Delete, LoadFromFile, SaveToFile, Count, Strings[], Text, Sort, Find, IndexOf, etc.) but requires no Create or Free — the compiler manages its lifetime automatically via an internal interface reference.

Use StringList instead of TStringList to avoid Create/Free boilerplate. It can be used as a local variable or as a field in classes or records. Unlike Vector/Matrix, StringList has no memory pool caching — each instance manages its own internal TStringList via interface reference counting.

// No Create, no Free, no try/finally
var sl: StringList;
begin
    sl.Add('line 1');
    sl.Add('line 2');
    sl.SaveToFile('output.txt');
end;  // freed automatically

StringList auto-converts to TStrings and TStringList via implicit operators, so it can be passed directly to any method expecting those types.

See also: topic type-selection for choosing between value types and class types.