CODEWITHSUNDEEP
c#.netreflectionsystem.reflection
Evelyn
Evelyn

Reputation: 81

Why does integer '0' IEquatable.Equals return true against a null object when called through reflection but false when called on the integer?

Calling IEquatable.Equals from an integer 0 to test against a null object should return false but when using reflection it returns true. Given the following code, I would expect for iEquals and equals to return 'false', but the reflection code returns true, why? I am on C# 7.3 and .NET Framework 4.6.2:

int zero = 0;
object nullObj = null;
var iEquals = zero.GetType().GetInterface("IEquatable`1").GetMethod("Equals");
var reflectionEquals = iEquals.Invoke(zero, new[] { nullObj }); // true
var equals = ((IEquatable<int>)zero).Equals(nullObj); // false

Upvotes: 3

Views: 110

Answers (1)

Guru Stron
Guru Stron

Reputation: 143078

From the MethodBase.Invoke docs:

If a parameter of the reflected method is a value type, and the corresponding argument in parameters is null, the runtime passes a zero-initialized instance of the value type.

For int zero-initialized instance is 0, hence True. Another example can be bool - for booleans zero-initialized instance is false so:

object nullObj = null;
bool zero = false;
var m = zero.GetType().GetInterface("IEquatable`1").GetMethod("Equals");
Console.WriteLine(m.Invoke(zero, new[]{nullObj})); // True

Demo @sharplab.io

Upvotes: 7

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