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Assign

procedure Assign(Source: TPersistent);

Example​

procedure CopyPersistent(const Source, Destination: TPersistent);
begin
  Destination.Assign(Source);
end;

Usage​

Requests a type-specific content copy and falls back through the source AssignTo protocol.

Parameters and result

Source must be a compatible live TPersistent. The destination remains the same object while its assignable values are copied or replaced.

Behaviour

  • Exact copied fields, object ownership and depth are defined by the destination/source item implementations.
  • Reference assignment (Destination := Source) aliases one object; Destination.Assign(Source) requests content copying.
  • Base fallback gives the source a chance to implement AssignTo for the destination type.
  • Self-assignment safety is type-specific; some list-like implementations can clear before copying.

Errors and edge cases

Nil source and unsupported source/destination combinations raise EConvertError in the base protocol. item conversion/allocation/callback errors propagate and may leave partial changes.

Additional Technical Info​

Assign is a script-visible method declared on hidden ancestor TPersistent. Visible descendant classes inherit it even though Classes/Common is intentionally omitted from the Velox and Docusaurus Code Library menus.

Assign asks the destination object to copy compatible content from Source. It copies object state according to descendant rules; it is not the same as assigning one object reference to another.

Implementation trace

PascalScript registers the virtual Delphi method. Studio 37.0's base TPersistent.Assign calls Source.AssignTo(Self) when Source is non-nil; nil calls AssignError. Descendants normally override Assign and may handle compatible types before falling back to this protocol.

Side effects and ownership

Can replace destination content, allocate/free owned subobjects and invoke descendant notifications. It does not transfer ownership of the Source object itself.

Performance and concurrency

Depends on descendant content size and copy depth; often O(n). No transaction, rollback or thread-safety guarantee.

Remarks

This entry describes the installed Delphi Studio 37.0 terminal reached by the Velox-modified PascalScript registration. Free Pascal is linked for compatible Object Pascal context; where implementations differ, the traced Delphi behaviour above is authoritative. The example is source-reviewed and non-destructive except where the named operation is inherently destructive.

Related entries

  • TObject.Free is lifetime destruction, not content assignment.
  • TCollection.Clear illustrates a destructive operation some descendant assignments can perform internally.

External references

Created 2026-07-15