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Dec

// Generated Code Library declaration:
procedure Dec;

// Effective call contract:
procedure Dec(var X);

Example​

procedure ScriptEvent(var Value: variant);
var
  Counter: Integer;
begin
  Counter := 5;
  Dec(Counter);
  Value := Counter; // 4
end;

Usage​

Decrements a supported integer variable by exactly one through Velox scripting's synthetic var parameter.

Parameters

NameTypeDescription
Xsupported integer variable, varValue changed in place. It must be assignable storage, not a literal or calculated expression.

Supported runtime storage types are Byte, ShortInt, Word, SmallInt, Cardinal, Integer, Int64 and UInt64. The effective parameter is untyped at script declaration, so unsupported types can compile but fail at runtime.

Boundary behaviour and quirks

  • Only a step of one is available. Dec(X, N) is part of Velox but not this script declaration.
  • Velox scripting.inc explicitly compiles this runtime with range and overflow checks off, overriding the enclosing project setting. Every supported fixed-width type wraps at its boundary: for example, Dec(Byte(0)) becomes 255, Dec(Low(Integer)) becomes High(Integer), and Dec(UInt64(0)) becomes High(UInt64).
  • The Cardinal branch passes through signed SetInt, but unchecked conversions preserve the low 32-bit pattern; valid high Cardinal values are not rejected.
  • Enumerations have a distinct Velox scripting btEnum base type and are not handled, despite Velox's broader ordinal contract.
  • A Variant is not handled. Use GetAndInc only for its specific increment-and-return Variant use case; there is no matching decrement helper.

Additional Technical Info​

Dec subtracts exactly one from a mutable PascalScript integer variable. The generated declaration is incomplete: the compiler adds a required untyped var X parameter after creating the displayed declaration.

This is a PascalScript runtime helper, not Delphi's full intrinsic contract. It has no second decrement-amount argument and does not support pointers, characters, enumerations or Variants through this registered path. The example is fictional and source-reviewed only.

Implementation

  1. The compiler adds the synthetic in/out parameter to the nominally parameterless declaration.
  2. Runtime Dec_ resolves the parameter by reference with NewTPSVariantIFC(..., True).
  3. It switches on the exact PascalScript base type, subtracts one and writes through a type-specific stack setter.
  4. An unsupported base type returns failure, which the script runtime reports as a call/type error.

This external helper is separate from the cm_dec bytecode used internally to advance a for..downto loop counter.

Side effects and concurrency

X is mutated in place. The operation has no lock or atomic interlocked semantics. Do not use it as a synchronization primitive for Globals shared by concurrent executions. Check the boundary explicitly if wraparound is not intended.

External references

Created 2026-07-15