C# Language Specification

Better conversion from type

Given a conversion C₁ that converts from a type S to a type T₁, and a conversion C₂ that converts from a type S to a type T₂, C₁ is a better conversion than C₂ if at least one of the following holds:

• 
  An identity conversion exists from S to T₁ but not from S to T₂
  
• 
  T₁ is a better conversion target than T₂ (§7.5.3.5)
  

5. Better conversion target

Given two different types T₁ and T₂, T₁ is a better conversion target than T₂ if at least one of the following holds:

• 
  An implicit conversion from T₁ to T₂ exists, and no implicit conversion from T₂ to T₁ exists
  
• 
  T₁ is a signed integral type and T₂ is an unsigned integral type. Specifically:
  

• 
  T₁ is sbyte and T₂ is byte, ushort, uint, or ulong
  
• 
  T₁ is short and T₂ is ushort, uint, or ulong
  
• 
  T₁ is int and T₂ is uint, or ulong
  
• 
  T₁ is long and T₂ is ulong
  

6.