klod68/gen-options-class

---

name: gen-options-class description: "Use when adding strongly-typed configuration to a .NET service or library. Generates an options interface, concrete class with sensible defaults, EnsureValid() startup validation, and the matching appsettings.json section. Also invoke when the user mentions: options class, IOptions, configuration class, appsettings section, settings class. Domain: Code Generation, Configuration. Level: Beginner."

Generate a validated options class for the feature: ${1:FeatureName}.

Context

• Namespace root: ${2:MyApp}
• Required properties (no sensible default — must be configured): ${3:e.g. ConnectionString string, ApiKey string}
• Optional properties (have defaults — safe if omitted): ${4:e.g. MaxRetryCount int 3 range 0-10, TimeoutSeconds int 30 range 1-300, EnableFeatureX bool true}
• Cross-property constraints (if any): ${5:e.g. MaxDelay must be >= InitialDelay, or none}

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Required output — generate ALL of the following:

1. Options interface

${2}.${1}.Configuration.I${1}Options.cs

• public interface with get; set; properties
• XML doc on the interface and every property

2. Options implementation

${2}.${1}.Configuration.${1}Options.cs

public sealed class ${1}Options : I${1}Options
{
    // ── Required (no default) ──────────────────────────
    public string ConnectionString { get; set; } = string.Empty;

    // ── Optional (sensible defaults) ──────────────────
    public int MaxRetryCount { get; set; } = 3;

    // ── Validation ────────────────────────────────────
    /// <summary>
    /// Validates that all required settings are present and all values are within
    /// valid ranges. Called eagerly by the composition root at startup.
    /// </summary>
    /// <exception cref="InvalidOperationException">Thrown when any setting is invalid.</exception>
    public void EnsureValid()
    {
        // Required: throw with actionable fix message
        if (string.IsNullOrWhiteSpace(ConnectionString))
            throw new InvalidOperationException(
                $"${1}Options.ConnectionString is required. " +
                $"Configure it with: Add${1}(o => o.ConnectionString = \"...\").");

        // Ranges: include actual value and valid range in message
        if (MaxRetryCount is < 0 or > 10)
            throw new InvalidOperationException(
                $"${1}Options.MaxRetryCount must be 0–10, but was {MaxRetryCount}.");

        // Cross-property (fill from context if provided)
    }
}

3. Matching appsettings.json section

Show the JSON block consumers add to their configuration, with every key, its default value (or empty string for required), and a comment explaining it.

4. Validation rules summary

Document in a table:

| Property | Required | Default | Valid range / constraint | Error message pattern | |---|---|---|---|---|

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Validation message rules

Every InvalidOperationException message must:

• Name the class and property (${1}Options.PropertyName)
• State the actual value for range violations
• State how to fix it (the configuration path or code to call)
• Never say "invalid value" without explaining what valid looks like

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Constraints

• Follow all rules in the workspace root instruction file
• EnsureValid() is the single validation entry point — no scattered if checks
• Options class is public sealed (crosses module boundary)
• Required string properties default to string.Empty — never null
• Numeric defaults are correct for the described use case — not arbitrary