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//
// Gendarme.Rules.Design.AvoidRefAndOutParametersRule
//
// Authors:
// Sebastien Pouliot <sebastien@ximian.com>
//
// Copyright (C) 2008, 2011 Novell, Inc (http://www.novell.com)
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
//
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//
using System;
using System.Globalization;
using Mono.Cecil;
using Gendarme.Framework;
using Gendarme.Framework.Rocks;
namespace Gendarme.Rules.Design {
/// <summary>
/// This rule fires if a method uses <c>ref</c> or <c>out</c> parameters.
/// These are advanced features that can easily be misunderstood and misused
/// (by the consumer). This can result in an API that is difficult to use so
/// avoid them whenever possible.
/// An alternative is to use one of the new generic <c>Tuple</c> types (FX v4 and later)
/// as the return value.
/// No defect will be reported if the method:
/// <list>
/// <item>follows the <c>bool Try*(X out)</c> pattern; or</item>
/// <item>implement an interface requiring the use of <c>ref</c> or <c>out</c> parameters.
/// In the later case defects will be reported against the interface itself (if analyzed
/// by Gendarme).</item>
/// </list>
/// </summary>
/// <example>
/// Bad example:
/// <code>
/// public bool NextJob (ref int id, out string display)
/// {
/// if (id < 0)
/// return false;
/// display = String.Format ("Job #{0}", id++);
/// return true;
/// }
/// </code>
/// </example>
/// <example>
/// Good example:
/// <code>
/// private int id = 0;
///
/// private int GetNextId ()
/// {
/// int id = this.id++;
/// return id;
/// }
///
/// public string NextJob ()
/// {
/// return String.Format ("Job #{0}", Id);
/// }
/// </code>
/// </example>
/// <remarks>This rule is available since Gendarme 2.0</remarks>
[Problem ("This method use ref and/or out parameters in a visible API which can confuse many developers.")]
[Solution ("The most common reason to do this is to return multiple values from a method which can be rewritten so that it returns a custom type instead.")]
[FxCopCompatibility ("Microsoft.Design", "CA1021:AvoidOutParameters")]
[FxCopCompatibility ("Microsoft.Design", "CA1045:DoNotPassTypesByReference")]
public class AvoidRefAndOutParametersRule : Rule, IMethodRule {
static bool IsSignatureDictatedByInterface (MethodDefinition method, TypeReference type)
{
if (type == null)
return false;
TypeDefinition td = type.Resolve ();
if (td == null)
return false;
foreach (InterfaceImplementation intf_ref in td.Interfaces) {
TypeDefinition intr = intf_ref.InterfaceType.Resolve ();
if (intr == null)
continue;
if (intr.HasMethods) {
foreach (MethodDefinition md in intr.Methods) {
if (method.CompareSignature (md))
return true;
}
}
// check if the interface inherits from another interface with this signature
if (IsSignatureDictatedByInterface (method, intr.BaseType))
return true;
}
// check if a base type is implementing an interface with this signature
return IsSignatureDictatedByInterface (method, td.BaseType);
}
static bool IsSignatureDictatedByInterface (MethodDefinition method)
{
// quick-out: if the method implements an interface then it's virtual
if (!method.IsVirtual)
return false;
// check if the interface itself has the defect (always reported)
TypeDefinition type = method.DeclaringType;
if (type.IsInterface)
return false;
return IsSignatureDictatedByInterface (method, type);
}
public RuleResult CheckMethod (MethodDefinition method)
{
// rule only applies to visible methods with parameters
// we also exclude all p/invokes since we have a rule for them not to be visible
if (method.IsPInvokeImpl || !method.HasParameters || !method.IsVisible ())
return RuleResult.DoesNotApply;
foreach (ParameterDefinition parameter in method.Parameters) {
string how = null;
if (parameter.IsOut) {
// out is permitted for the "bool Try* (...)" pattern
if (method.ReturnType.IsNamed ("System", "Boolean") &&
method.Name.StartsWith ("Try", StringComparison.Ordinal)) {
continue;
}
how = "out";
} else if (parameter.ParameterType.IsByReference) {
how = "ref";
}
// report the method is it is not dictated by an interface
if ((how != null) && !IsSignatureDictatedByInterface (method)) {
// goal is to keep the API as simple as possible so this is more severe for public than protected methods
Severity severity = method.IsPublic ? Severity.Medium : Severity.Low;
string msg = String.Format (CultureInfo.InvariantCulture,
"Parameter '{0}' passed by reference ({1}).", parameter.Name, how);
Runner.Report (parameter, severity, Confidence.Total, msg);
}
}
return Runner.CurrentRuleResult;
}
}
}
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