This session will introduce developers to the new powerful new feature that is part of the .NET 4.5 framework called Code Contracts. Code Contracts brings the advantages of design-by-contract programming to .NET programming. Contracts are used to improve testing via run-time checking, enable static contract verification, and documentation generation.
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9.
Always check for valid parameter
arguments!
Perform argument validation for every public
or protected method
Throw meaningful exceptions to the
developer for invalid parameter arguments
Use the System.ArgumentException class
Or your own class derived from
System.ArgumentException
10. public string FormatPhoneNumber(string str, bool bTakeOutDash)
{
string str1 = str.Trim();
if (bTakeOutDash)
{
if (11 == str.Length && -1 != str.IndexOf('-'))
{
str1 = "";
for (int i = 0; i < str.Length; i++)
{
if ("-" != str.Substring(i, 1))
{
str1 = string.Concat(str1, str.Substring(i, 1));
}
}
}
}
return str1;
}
11. public string FormatPhoneNumber(string str, bool bTakeOutDash)
{
if (string.IsNullOrWhiteSpace(str))
{
throw new ArgumentNullException("str", "Phone number must be supplied.");
}
string str1 = str.Trim();
if (bTakeOutDash)
{
// Code Removed for brevity
}
return str1;
}
13.
Is an approach for designing software.
It prescribes that software designers should
define formal, precise and verifiable interface
specifications for software components, which
extend the ordinary definition of abstract data
types with preconditions, post-conditions and
invariants.
These specifications are referred to as
"contracts", in accordance with a conceptual
metaphor with the conditions and obligations of
business contracts.
14.
A discipline of
analysis, design, implementation, management
Applications throughout the software lifecycle:
Getting the software right:
analysis, design , implementation
Debugging & testing
Automatic documentation
Getting inheritance right
Getting exception handling right!
Maintenance
Management
15.
Every software element is intended to
satisfy a certain goal, or contract
For the benefit of other software elements (and
ultimately of human users)
The contract of any software element should
be
Explicit
Part of the software element itself
16. Precondition
What does it expect?
Postcondition
What does it promise?
What does it maintain?
Class
invariant
17.
New API + tools from Microsoft for Designby-Contract
System.Diagnostics.Contracts
MSIL rewriting
Inspired by Spec#
Included in .NET 4.0/ 4.5
Latest version released 9/13
http://research.microsoft.com/en-us/projects/contracts/
19.
Usually for method parameter checking
Caller’s responsibility to make sure the
precondition is true on entry into method
Does not need to be compiled in production
code
Can also include throwing of Exceptions
These must be compiled into assembly
26.
Postconditions are contracts for the state of
a method when it terminates
The postcondition is checked just before
exiting a method
The run-time behavior of failed
postconditions is determined by the runtime
analyzer.
31.
ContractInvariantMethod
Mark methods that contain object invariant
specifications
The methods marked with this attribute must
be nullary methods with void return types and
contain nothing other than calls to Contract
You may not call these methods from within
your code.
Force coders to do proper value checking!
32. public Int32 Value
{
get { return _value; }
private set
{
if (this.Value != value)
{
if ((value <= this.Maximum) && (value >= this.Minimum))
{
this._value = value;
this.OnValueChanged();
}
}
}
}
33. public Int32 Value
{
get { return _value; }
private set
{
if (this.Value != value)
{
Contract.Requires<ArgumentOutOfRangeException>(value >= 0);
if ((value <= this.Maximum) && (value >= this.Minimum))
{
this._value = value;
this.OnValueChanged();
}
}
}
}
34. private Int32 _value;
[ContractInvariantMethod]
private void Invariants()
{
Contract.Invariant(_value >= 0,
"Value cannot be less than zero.");
}
-------------------------------------set
{
// Contract.Requires<ArgumentOutOfRangeException>(value >= 0);
if (this.Value != value)
{
// Code Removed for Brevity
}
}
37.
Pex and Moles
Isolation and White box Unit Testing for .NET
Pex auto generates test suites with high code
coverage
Moles supports unit testing by way of detours
and stubs (delegates)
http://research.microsoft.com/en-us/projects/pex/