Is there an IDictionary implementation that, on missing key, returns the default value instead of throwing?

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Indeed, that won’t be efficient at all.

As per comments, in .Net Core 2+ / NetStandard 2.1+ / Net 5, MS added the extension method GetValueOrDefault()

For earlier versions you can write the extension method yourself:

public static TValue GetValueOrDefault<TKey,TValue>
    (this IDictionary<TKey, TValue> dictionary, TKey key)
{
    TValue ret;
    // Ignore return value
    dictionary.TryGetValue(key, out ret);
    return ret;
}

Or with C# 7.1:

public static TValue GetValueOrDefault<TKey,TValue>
    (this IDictionary<TKey, TValue> dictionary, TKey key) =>
    dictionary.TryGetValue(key, out var ret) ? ret : default;

That uses:

  • An expression-bodied method (C# 6)
  • An out variable (C# 7.0)
  • A default literal (C# 7.1)

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