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Conditional selection

The Conditional selection group provides compact fallback and two-value selection functions. Similar names are not synonyms: each entry has its own trigger test, result type and Variant conversion path.

Choosing an entry​

  • Use IfNull when the first Variant's exact Null-comparison behavior is the intended trigger and the selected Variant type should be preserved.
  • Use CoalesceEmpty when Velox's broader null/empty/trimmed-blank predicate and a text result are required.
  • Use CoalesceString or IfBlank only for their exact-empty typed-string behavior; whitespace is not blank to those implementations despite one public name.
  • Use CoalesceFloat or CoalesceInteger when the selected value must be converted to that numeric type.
  • Use IfThen for Boolean selection between two string values.

Null, Empty and blank are different​

Velox scripts can encounter Variant Null, Empty/clear values, empty text, whitespace-only text, numeric zero and Boolean False. The child pages contain the verified trigger and conversion tables. Do not replace one helper with another based only on its name.

Some implementations compare a Variant directly with Null; their behavior can be affected by Delphi's process-wide Variant rules. Others convert through VarToStr, trim text or perform a numeric Variant conversion, any of which can raise or invoke a custom Variant handler.

Eager evaluation​

These are functions, not language-level short-circuit constructs. PascalScript evaluates supplied arguments before entering the function. A fallback expression can therefore query data, mutate state or raise even when the function ultimately returns the preferred value.

Use an if statement when evaluation itself must be conditional:

if VarIsNull(Value) then
  Value := BuildFallback;

The example is illustrative; choose the predicate that matches the actual data contract. See Testing values for the differences among Variant states and safe guard patterns.