What does [param: NotNull] mean in C#?
param:
is the attribute target. See: Attribute specification
The attribute target can be one of these:
assembly, module, field, event, method, param, property, return, type
So [param: NotNull]
means that the NotNullAttribute
applies to the value
parameter of the setter. It is necessary to specify the target here, since the value
parameter does not appear as a method parameter explicitly.
A common use of the attribute-target is to specify the InternalsVisibleToAttribute
in order to make types and members declared as internal
visible to unit test projects.
[assembly:InternalsVisibleTo("UnitTestProject")]
The assembly does not appear as a language construct, therefore the attribute-target assembly
is the only way to specify an attribute for the assembly. Btw: It can be specified in any source code file.
When you mark method with NotNull
it means, that method returns not null object:
[NotNull]
public object Get()
{
return null; //error
}
When you mark setter it does the same - setter returns not null (because .net converts properties to get and set methods).
public virtual IRelationalTransaction Transaction { get; [NotNull] protected set; }
Equals to:
[NotNull]
public virtual void set_Transaction(IRelationalTransaction value) { ... }
So, you need to add param:
to point, that "i mean - parameter of setter is not null, not a result of set-method":
public virtual IRelationalTransaction Transaction { get; [param: NotNull] protected set; }
Equals to:
public virtual void set_Transaction([NotNull] IRelationalTransaction value) { ... }