ReflectionIT.PropertyThrowGenerator

ReflectionIT.PropertyThrowGenerator is a source generator that adds validation to partial properties annotated with [ThrowIf...] attributes.

The generated setters call the appropriate Argument...Exception.ThrowIf... helper methods before assigning the value.

NuGet package

Package	Version
ReflectionIT.PropertyThrowGenerator

Requirements

• LangVersion must be C# 14.0 or higher because the generated code uses the field keyword.
• TargetFramework must be .NET 8.0 or higher because the generated code uses ArgumentOutOfRangeException throw helper methods.

How it works

1. Add the NuGet package to your project.
2. Annotate a partial property with one or more [ThrowIf...] attributes.
3. The generator emits the implementation part of the property and inserts the required validation logic into the set or init accessor.

If a ThrowIf... attribute is used on a non-partial property, the analyzer reports a diagnostic.

Example

After installing the package, write code like this:

using ReflectionIT.PropertyThrowGenerator.Attributes;

partial class Employee {

    [ThrowIfNull]
    public required partial string Name { get; set; }

    [ThrowIfNull]
    [ThrowIfGreaterThan("London")]
    public partial string City { get; set; } = string.Empty;

    [ThrowIfLessThanOrEqual(17)]
    public partial int Age { get; set; }

    // Decimal attribute arguments are not supported directly, so use a string literal instead.
    [ThrowIfGreaterThan("1234.56M")]
    [ThrowIfNegative]
    public partial decimal Salary { get; set; }

}

This generates a partial class with four validated properties:

partial class Employee
{
    public required partial string Name {
        get;
        set {
            global::System.ArgumentNullException.ThrowIfNull(value);
            field = value;
        }
    }

    public partial string City {
        get;
        set {
            global::System.ArgumentNullException.ThrowIfNull(value);
            global::System.ArgumentOutOfRangeException.ThrowIfGreaterThan(value, "London");
            field = value;
        }
    }

    public partial int Age {
        get;
        set {
            global::System.ArgumentOutOfRangeException.ThrowIfLessThanOrEqual(value, 17);
            field = value;
        }
    }

    public partial decimal Salary {
        get;
        set {
            global::System.ArgumentOutOfRangeException.ThrowIfGreaterThan(value, 1234.56M);
            global::System.ArgumentOutOfRangeException.ThrowIfNegative(value);
            field = value;
        }
    }
}

CommunityToolkit.MVVM ObservableProperty

You can also combine this source generator with the partial properties support from the .NET Community Toolkit 8.4

The MVVM Toolkit source generators have support for partial properties so if you use them this source generator can't generate the same partial properties any more. Luckily the toolkit also generates On...Changing partial methods. This source generator will generate this method instead. It contains the Argument...Exception.ThrowIf... method calls.

In the next example the partial properties of the Employee class have the ObservableProperty and ThrowIf... attributes.

partial class Employee {
                
    [ThrowIfNull]
    [CommunityToolkit.Mvvm.ComponentModel.ObservableProperty]
    public required partial string Name { get; init; }

    [ThrowIfGreaterThan("1234.56M")]
    [ThrowIfNegative]
    [CommunityToolkit.Mvvm.ComponentModel.ObservableProperty]                       
    public partial decimal Salary { get; set; }
}

This generates a partial class with the OnNameChanging and OnSalaryChanging methods containing the Argument...Exception.ThrowIf....

partial class Employee
{
    partial void OnNameChanging(string value) {
        global::System.ArgumentNullException.ThrowIfNull(value);
    }

    partial void OnSalaryChanging(decimal value) {
        global::System.ArgumentOutOfRangeException.ThrowIfGreaterThan(value, 1234.56M);
        global::System.ArgumentOutOfRangeException.ThrowIfNegative(value);
    }

}

Attributes

• ThrowIfEqualAttribute
• ThrowIfGreaterThanAttribute
• ThrowIfGreaterThanOrEqualAttribute
• ThrowIfLessThanAttribute
• ThrowIfLessThanOrEqualAttribute
• ThrowIfNegativeAttribute
• ThrowIfNegativeOrZeroAttribute
• ThrowIfNotEqualAttribute
• ThrowIfNullAttribute
• ThrowIfNullOrEmptyAttribute
• ThrowIfNullOrWhiteSpaceAttribute
• ThrowIfZeroAttribute

Analyzer rules

The package also includes analyzers that help detect unsupported usage at compile time.

Rule ID	Severity	Description
PTG001	Error	Reported when the project uses a C# language version lower than 14.0.
PTG002	Error	Reported when a ThrowIf... attribute is applied to a property that is not declared partial.

PTG001: C# language version is not supported

This rule is reported when the consuming project does not use C# 14.0 or later.

The generator requires C# 14 because the generated code uses the field keyword.

PTG002: ThrowIf attributes require partial properties

This rule is reported when one of the ThrowIf... attributes is used on a property that is not declared partial.

Only partial properties are supported because the generator emits the implementation part of the property.

License

This project is licensed under the MIT License - see the LICENSE file for details.