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IsValidDateWeek

Function IsValidDateWeek(const AYear, AWeekOfYear, ADayOfWeek: Word): Boolean

Example​

procedure ScriptEvent(var Value: variant);
begin
  Value := IsValidDateWeek(2026, 1, 1); // True
end;

Usage​

IsValidDateWeek validates an ISO week-numbering year, week and Monday-based weekday.

Parameters

NameTypeDescription
AYearWord, constISO week-numbering year; valid range 1 through 9999.
AWeekOfYearWord, constOne-based ISO week number.
ADayOfWeekWord, constMonday-based weekday; 1 is Monday and 7 is Sunday.

Returns

True when the year is supported, the week is 1 through that year's ISO week count, and the weekday is 1 through 7.

Behaviour

  • Week 1 follows ISO week-numbering rules rather than simply starting on 1 January.
  • Week 53 is accepted only for a year for which WeeksInAYear returns 53.
  • Weekdays are Monday 1 through Sunday 7.

Important usage notes

  • The ISO week-numbering year near New Year can differ from the calendar year of the resulting date.
  • Zero is invalid for the week and weekday; Word prevents negative arguments.
  • This checks the field tuple but does not return its corresponding calendar date.

Usage notes

Use the result as the documented field or date predicate only. It does not establish a timezone, business calendar or input provenance.

Additional Technical Info​

IsValidDateWeek validates an ISO week-numbering year, week and Monday-based weekday.

The example is fictional and source-reviewed. It is deterministic for the supplied fields. It was not executed by the documentation workflow.

Implementation

The DateUtils import binds directly to Delphi 37.0 System.DateUtils.IsValidDateWeek. It validates the year, compares the week with WeeksInAYear(AYear) and directly checks the weekday range.

Side effects

None.

Errors

There is no wrapper exception handling. Ordinary out-of-range Word fields return False rather than raising.

Performance and concurrency

Constant-time field decoding or comparison with no external I/O. The routine uses no shared mutable state.

Related entries

External references

Created 2026-07-15