Humanizr/Humanizer · error · NotSupportedException

The configured ITimeSpanHumanizeStrategy does not support gr

Error message

The configured ITimeSpanHumanizeStrategy does not support grammatical-case-aware durations.

What it means

Thrown by HumanizeWithCase when the configured ITimeSpanHumanizeStrategy (set via Configurator.TimeSpanHumanizeStrategy) does not also implement IGrammaticalCaseTimeSpanHumanizeStrategy. Grammatical-case-aware duration output requires the strategy to support case selection, which is an opt-in interface beyond the base ITimeSpanHumanizeStrategy.

Source

Thrown at src/Humanizer/TimeSpanHumanizeExtensions.cs:118

    /// <param name="collectionSeparator">The separator used to combine time parts. If null, the culture's default collection formatter is used.</param>
    /// <returns>The locale-authored unit-case phrase. The count may be written explicitly or encoded by the unit form.</returns>
    /// <exception cref="ArgumentOutOfRangeException"><paramref name="grammaticalCase"/> is not defined.</exception>
    /// <exception cref="NotSupportedException">The configured strategy, selected formatter, locale, or duration unit does not support the requested case.</exception>
    public static string HumanizeWithCase(
        this TimeSpan timeSpan,
        GrammaticalCase grammaticalCase,
        int precision,
        bool countEmptyUnits,
        CultureInfo? culture = null,
        TimeUnit maxUnit = TimeUnit.Week,
        TimeUnit minUnit = TimeUnit.Millisecond,
        string? collectionSeparator = ", ")
    {
        ValidateGrammaticalCase(grammaticalCase);

        if (Configurator.TimeSpanHumanizeStrategy is not IGrammaticalCaseTimeSpanHumanizeStrategy strategy)
        {
            throw new NotSupportedException(
                $"The configured {nameof(ITimeSpanHumanizeStrategy)} does not support grammatical-case-aware durations.");
        }

        return strategy.Humanize(
            timeSpan,
            precision,
            countEmptyUnits,
            culture,
            maxUnit,
            minUnit,
            collectionSeparator,
            false,
            grammaticalCase);
    }

    /// <summary>
    /// Turns a <see cref="TimeSpan"/> into a human readable form using localized unit symbols.
    /// </summary>

View on GitHub (pinned to ffc2b77c0f)

Solutions

1. Make your custom strategy implement IGrammaticalCaseTimeSpanHumanizeStrategy.
2. Restore the default strategy (DefaultTimeSpanHumanizeStrategy) which supports cases.
3. Avoid calling HumanizeWithCase when using a strategy that doesn't support it.

Example fix

// before
public class MyStrategy : ITimeSpanHumanizeStrategy
{
    public string Humanize(TimeSpan ts, int p, bool c, CultureInfo? cult, TimeUnit max, TimeUnit min, string? sep, bool words, bool symbols) => ...
}

// after
public class MyStrategy : ITimeSpanHumanizeStrategy, IGrammaticalCaseTimeSpanHumanizeStrategy
{
    public string Humanize(TimeSpan ts, int p, bool c, CultureInfo? cult, TimeUnit max, TimeUnit min, string? sep, bool words, bool symbols) => ...
    public string Humanize(TimeSpan ts, int p, bool c, CultureInfo? cult, TimeUnit max, TimeUnit min, string? sep, bool symbols, GrammaticalCase gc) => ...
}

static bool StrategySupportsCase(ITimeSpanHumanizeStrategy strategy) =>
    strategy is IGrammaticalCaseTimeSpanHumanizeStrategy;

static bool CanHumanizeWithCase(ITimeSpanHumanizeStrategy strategy) =>
    strategy is IGrammaticalCaseTimeSpanHumanizeStrategy;

When it happens

Trigger: Registering a custom ITimeSpanHumanizeStrategy via Configurator.TimeSpanHumanizeStrategy and then calling timeSpan.HumanizeWithCase(GrammaticalCase.Genitive). The check at line 116 tests the type and throws.

Common situations: Replacing the default strategy with a custom implementation for logging, caching, or experimentation, without implementing the case-aware interface. Upgrading Humanizer and discovering new case APIs that the old custom strategy doesn't support.

Related errors

• Custom strategy type '{GetType().FullName}' must explicitly
• Grammatical case is not supported for time-unit symbols.
• The formatter for '{culture?.Name ?? CultureInfo.CurrentCult
• Custom formatter type '{GetType().FullName}' must explicitly
• Culture '{Culture.Name}' has no grammatical-case classificat

AI-assisted analysis of Humanizr/Humanizer@ffc2b77c0f (2026-08-13). Data as JSON: /api/errors/d549051c80ef6324. Report an issue: GitHub.