/// <summary>
/// Generates a new hash code function.
/// </summary>
/// <param name="typeBuilder">The type builder to use.</param>
/// <param name="fieldsToUse">All fields to use to compute the hash code.</param>
/// <returns>The created hash code function.</returns>
public static MethodInfo GenerateHashCode(
this TypeBuilder typeBuilder,
FieldInfo[] fieldsToUse)
{
var getHashCode = typeBuilder.DefineMethod(
GetHashCodeInfo.Name,
MethodAttributes.Public | MethodAttributes.Virtual,
typeof(int),
Array.Empty <Type>());
var emitter = new ILEmitter(getHashCode.GetILGenerator());
var result = emitter.DeclareLocal(typeof(int));
emitter.EmitConstant(0);
emitter.Emit(LocalOperation.Store, result);
foreach (var field in fieldsToUse)
{
emitter.Emit(LocalOperation.Load, result);
emitter.Emit(OpCodes.Ldarg_0);
var fieldHashCode = field.FieldType.GetMethod(
GetHashCodeInfo.Name,
BindingFlags.Public | BindingFlags.Instance);
if (!field.FieldType.IsValueType)
{
emitter.Emit(OpCodes.Ldfld, field);
}
else if (fieldHashCode.DeclaringType != field.FieldType)
{
// to call GetHashCode inherited from ValueType, struct must be boxed
emitter.Emit(OpCodes.Ldfld, field);
emitter.Emit(OpCodes.Box, field.FieldType);
}
else
{
emitter.Emit(OpCodes.Ldflda, field);
}
emitter.EmitCall(fieldHashCode);
emitter.Emit(OpCodes.Xor);
emitter.Emit(LocalOperation.Store, result);
}
emitter.Emit(LocalOperation.Load, result);
emitter.Emit(OpCodes.Ret);
emitter.Finish();
typeBuilder.DefineMethodOverride(getHashCode, GetHashCodeInfo);
return(getHashCode);
}
