Welcome to CoreConditions

CoreConditions is a library that helps developers to write pre- and postcondition validations in their .NET applications. This is a fork of CuttingEdge.Conditions created by dotnetjunkie in order to make it compatible with .NET Core.

Overview

CoreConditions is build up upon the C# and VB.NET extension method mechanism and it allows you to validate arguments in a simple and fluent way. The following example gives a quick overview on the way you could write your pre- and postconditions.

C# example

public ICollection GetData(Nullable<int> id, string xml, IEnumerable<int> col)
{
    // Check all preconditions:
    Condition.Requires(id, nameof(id))
        .IsNotNull()          // throws ArgumentNullException on failure
        .IsInRange(1, 999)    // ArgumentOutOfRangeException on failure
        .IsNotEqualTo(128);   // throws ArgumentException on failure

    Condition.Requires(xml, nameof(xml))
        .StartsWith("<data>") // throws ArgumentException on failure
        .EndsWith("</data>")  // throws ArgumentException on failure
        .Evaluate(xml.Contains("abc") || xml.Contains("cba")); // arg ex

    Condition.Requires(col, nameof(col))
        .IsNotNull()          // throws ArgumentNullException on failure
        .IsEmpty()            // throws ArgumentException on failure
        .Evaluate(c => c.Contains(id.Value) || c.Contains(0)); // arg ex

    // Do some work

    // Example: Call a method that should not return null
    object result = BuildResults(xml, col);

    // Check all postconditions:
    Condition.Ensures(result, nameof(result))
        .IsOfType(typeof(ICollection)); // throws PostconditionException on failure

    return (ICollection)result;
}
    
public static int[] Multiply(int[] left, int[] right)
{
    Condition.Requires(left, nameof(left)).IsNotNull();
    
    // You can add an optional description to each check
    Condition.Requires(right, nameof(right))
        .IsNotNull()
        .HasLength(left.Length, "left and right should have the same length");
    
    // Do multiplication
}

VB.NET example

Public Function GetData(ByVal id As Integer?, ByVal xml As String, _
    ByVal col As ICollection) As ICollection
    ' Check all preconditions:
    Condition.Requires(id, nameof(id)).IsNotNull().IsInRange(1, 999).IsNotEqualTo(128)
    
    Condition.Requires(xml, nameof(xml)).StartsWith("<data>").EndsWith("</data>")
    
    Condition.Requires(col, nameof(col)).IsNotNull().IsEmpty()
    
    ' Do some work
   
    ' Example: Call a method that should not return null
    Dim result = BuildResults(xml, col)
    
    ' Check all postconditions:
    Condition.Ensures(result, "result").IsOfType(GetType(ICollection))
    
    Return result
End Function
    
Public Shared Function Multiply(left As Integer(), right As Integer()) As Integer()
    left.Requires("left").IsNotNull()
    
    ' You can add an optional description to each check
    right.Requires("right").IsNotNull() _
        .HasLength(left.Length, "left and right should have the same length")
    
    ' Do multiplication
End Function

The previous example showed some important features of the library. The example showed the library's ability to:

• do precondition checks by writing Condition.Requires;
• do postcondition checks by writing Condition.Ensures;
• fluently chain calls to the validation methods, just separated by a dot;
• work with nullable data types;
• validate string objects;
• validate collections;
• do a type check on the variable.

Note: A particular validation is executed immediately when it's method is called, and therefore all checks are executed in the order in which they are written.

Getting started

CoreConditions is available as NuGet package.