How Does C# Resolve Overloaded Constructors When a Null Value is Passed?

Analysis of multi-loaded constructors and null parameters in C#

Suppose a class contains multiple constructors:

<code class="language-csharp">public class EffectOptions
{
    public EffectOptions(params object[] options) { }

    public EffectOptions(IEnumerable<object> options) { }

    public EffectOptions(string name) { }

    public EffectOptions(object owner) { }

    public EffectOptions(int count) { }

    public EffectOptions(Point point) { }
}</code>

When calling a constructor with a null value, such as EffectOptions options = new EffectOptions(null);, the overload resolution system will follow the following steps:

1. Identify applicable constructors:

• Identifies all accessible constructors.

2. Exclude unapplicable constructors:

• Delete any constructor whose formal parameters have no corresponding actual parameters, or whose actual parameters cannot be implicitly converted to the formal parameter type.

3. Parse params constructor:

• If a "params" constructor applies in both expanded and unexpanded forms, discard the expanded form.

4. Identify the best applicable candidates:

• "More specific" is better than "less specific".
• Start with the least specific candidate and gradually eliminate less specific candidates until only one "most specific" candidate remains.

In this case, the ambiguity arises because:

• object[] and string are both considered "specific" (there is no more specific in between).

Algorithm details:

• The actual algorithm is very complex.
• However, the general principle is that the more specific takes precedence over the less specific.

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