StrictlyTyped.Common 1.23.10508.12101-beta

Strictly Typed

What is it?

Strictly Typed is a library of interfaces and extensions that allow developers to strictly type simple primitive values. Using strictly typed values eliminates certain classes of errors and potential bugs from code. You can't mix up two Guid arguments to a method if they are of different types! You can also implement domain-specific functionality on types, or allow conversions or other operations, such as making it impossible to add NumberOfDays to NumberOfPlanets because those operations are meaningless. Note that if you want that operation, you can add it (by implementing, say, public static Z operator +(X left, Y right)). But by default, that sort of thing just doesn't happen.

What do I do with it?

This library is intended to be used with the Strictly Typed Generator (not included in this package), which generates strictly typed immutable value record structs from stubs annotated with marker Attributes.

For example, the Generator will generate an Employee Id type from this stub:

[StrictGuid] public partial record struct EmployeeId;

Note that the part you write must be partial, the Source Generator will implement the rest.

The namespace will be preserved, as will any enclosing types (static or non-static). Note that any enclosing types must also be partial, lest you anger Roslyn by causing the Source Generator to generate conflicting non-partial types. like so:

public static partial class Employee
{
    [StrictGuid] public partial record struct Id;
}

This will generate a strictly typed Guid of type Employee.Id.

These types implement a TypeConverter, so they will convert transparently to and from primitive types for, say, ASP .Net model binding for action methods. They also serialize and deserialize to and from Json transparently using System.Text.Json, so if , say, your web client application uses javascript in AJAX it is not necessary to do any conversions. The serialization and deserialization will take care of mapping the strict types to the correct primitive types.

But I want more control over my values!

These strict types use partial methods to provide options for manipulating values and validating them. For example,

[StrictGuid]
public partial record struct HasAnOverriddenToString
{
    static partial void _overrideToString(Guid value, ref string result)
    {
        result = $"Overridden {value}";
    }
}

This will cause the HasAnOverriddenToString's ToString() method to return Overridden 7240837c-757e-4c02-b592-28b7c24132c6 for a value that contains the Guid 7240837c-757e-4c02-b592-28b7c24132c6.

There are other partial methods which can be implemented, depending on the wrapped primitive type. For example, the StrictGuid types allow overrides for the following:

/// <summary>
/// If implemented, the wrapped value will be preprocessed by this method before creation
/// Preprocessing runs before validation (if implemented)
/// </summary>
/// <param name="value">The value which is to be preprocessed</param>
static partial void _preprocess(ref global::System.Guid result);

/// <summary>
/// If implemented, the result of calling CompareTo on the wrapped value will be modified by this method
/// </summary>
/// <param name="result">The value which will be returned by CompareTo</param>
partial void _overrideEquals(AStrictGuid? obj, ref global::System.Boolean result);

/// <summary>
/// If implemented, the result of calling ToString on the wrapped value will be modified by this method
/// </summary>
/// <param name="result">The value which will be returned by ToString</param>
static partial void _overrideToString(global::System.Guid value, ref global::System.String result);

/// <summary>
/// If implemented, the result of calling CompareTo on the wrapped value will be modified by this method
/// </summary>
/// <param name="result">The value which will be returned by CompareTo</param>
partial void _overrideCompareTo(global::System.Object? obj, ref global::System.Int32 result);

/// <summary>
/// If implemented, this method will be used to check that the value is valid.
/// Validation runs after preprocessing (if implemented)
/// If errors contains any values validation will be considered to have failed.
/// (note that using the constructor, Create, or cast operators will not use this method)
/// </summary>
/// <param name="errors">A set of reasons why the value fails validation</param>
partial void _validate(ref global::System.Collections.Generic.HashSet<global::System.String> errors);

So once I've defined a type, how to I get one of these values?

For [StrictString] public partial record struct FirstName;

No Validation Or Preprocessing

• Implicit cast (this is the most common one)

FirstName firstName = "Michael";

• Explicit cast

FirstName firstName = (FirstName)"Michael";

• Create static method

FirstName firstName = FirstName.Create("Michael");

• Constructor

FirstName firstName = new ("Michael");

Preprocessing, No Validation

• From static method

FirstName firstName = FirstName.From("Michael");

• As Extension

FirstName firstName = "Michael".As<FirstName>();

• AsNullable Extension (allows nulls, if the value passed in is null)

FirstName? firstName = "Michael".AsNullable<FirstName>();
FirstName? noFirstName = null.AsNullable<FirstName>();

Preprocessing and Validation

• TryAs Extension (without validation result out parameter)

if ("Michael".TryAs(out FirstName result)) { /* ... */ }

• TryAs Extension (with validation result out parameter)

if ("Michael".TryAs(out FirstName result, out IReadOnlySet<string> failures)) { /* ... */ }

• TryAsNullable Extension (allows nulls if the value passed in is null with validation result out parameter)

if ("Michael".TryAsNullable(out FirstName? result, out IReadOnlySet<string> failures)) { /* ... */ }

• TryFrom static method (without validation result out parameter)

if (FirstName.TryFrom("Michael", out FirstName result)) { /* ... */ }

• TryFrom static method (with validation result out parameter)

if (FirstName.TryFrom("Michael", out FirstName result, out IReadOnlySet<string> failures)) { /* ... */ }

Note that validation can always be performed on any instance by calling .Validate() Yes, that's quite a few ways of getting values. I almost always use implicit cast or a TryAs extension, but testing with other developers has resulted in the varied ways to create values here.

What about JSON support?

These types serialize and deserialize exactly like the types they wrap. There are currently two leading libraries that handle JSON support for C#. System.Text.Json: This is supported by default. Newtsonsoft.Json: This is supported, but you must add the following build symbol:

• USE_NEWTONSOFT_JSON You can add a build symbol through the Visual Studio package properties UI, or like this in the .csproj file.
• <DefineConstants>$(DefineConstants);USE_NEWTONSOFT_JSON</DefineConstants>

Does this work with Swagger?

Yes, there's a separate package that adds support for Swagger (not included in this package).

Does this work with Entity Framework?

Yes, there's a separate package that adds support for Entity Framework (not included in this package). The Source Generator also generates an EFConverter which you can enable in the declaring project by adding the USE_EF_CORE build symbol.

No really, how do I use this?

Look in the Github repo (url) and you'll find there's an Example project that is a slight adaptation of one of the simple Microsoft WebAPI tutorial projects.

What is included?

• StrictBool
• StrictByte
• StrictDecimal
• StrictDouble
• StrictFloat
• StrictHalf
• StrictInt
• StrictLong
• StrictSByte
• StrictShort
• StrictString
• StrictUInt
• StrictULong
• StrictUShort

What is not included (yet)?

The following are on my to-do list:

• StrictDateTime
• StrictDateOnly
• StrictTimeOnly
• Strict<T>

Acknowledgements

This project has been heavily influenced by the code, articles, books, videos, blog posts, StackOverflow answers, and tutorials by (in no particular order)

• Vladimir Khorikov
• Andrew Lock
• Zoran Horvat

In particular, Andrew Lock's excellent Strongly Typed IDs project showed me how to solve the problem of Entity Framework forcing evaluation on the server rather than the database. The blog post series accompanying it helped file a lot of rough edges off my source generator project. I doubt I would have been able to finish without such a clear guide to making source generators work.

Get in touch!

Contact the developer, "DMJ", at david.markham.jones@gmail.com