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https://github.com/k94ll13nn3/AutoConstructor
C# source generator that generates a constructor from readonly fields/properties in a class or struct
https://github.com/k94ll13nn3/AutoConstructor
constructor csharp csharp-sourcegenerator dotnet roslyn source-generator
Last synced: about 2 months ago
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C# source generator that generates a constructor from readonly fields/properties in a class or struct
- Host: GitHub
- URL: https://github.com/k94ll13nn3/AutoConstructor
- Owner: k94ll13nn3
- License: mit
- Created: 2021-03-02T19:33:36.000Z (over 3 years ago)
- Default Branch: main
- Last Pushed: 2024-08-01T06:41:34.000Z (about 2 months ago)
- Last Synced: 2024-08-01T08:15:49.339Z (about 2 months ago)
- Topics: constructor, csharp, csharp-sourcegenerator, dotnet, roslyn, source-generator
- Language: C#
- Homepage:
- Size: 453 KB
- Stars: 41
- Watchers: 3
- Forks: 4
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- License: LICENSE
Awesome Lists containing this project
- RSCG_Examples - https://github.com/k94ll13nn3/AutoConstructor
- csharp-source-generators - AutoConstructor -   C# source generator that generates a constructor from readonly fields/properties in a class or struct. (Source Generators / Other)
README
# AutoConstructor
[](https://www.nuget.org/packages/AutoConstructor/)
[](https://github.com/k94ll13nn3/AutoConstructor/releases/latest)
[](https://raw.githubusercontent.com/k94ll13nn3/AutoConstructor/main/LICENSE)
C# source generator that generates a constructor from readonly fields/properties in a class or struct.
## Installation
- Grab the latest package on [NuGet](https://www.nuget.org/packages/AutoConstructor/).
## Requirements
| Version | Visual Studio | .NET SDK |
|---------|---------------|----------|
| <=1.3.0 | 16.10+ | 5.0.300+ |
| >=2.0.0 | 17.0+ | 6.0.100+ |
| >=5.0.0 | 17.6+ | 7.0.302+ |
## Basic usage
The following code:
```csharp
[AutoConstructor]
public partial class MyClass
{
private readonly MyDbContext _context;
private readonly IHttpClientFactory _clientFactory;
private readonly IService _service;
[AutoConstructorInject("options?.Value", "options", typeof(IOptions))]
private readonly ApplicationOptions _options;
}
```
will generate:
```csharp
//------------------------------------------------------------------------------
//
// This code was generated by the AutoConstructor source generator.
//
// Changes to this file may cause incorrect behavior and will be lost if
// the code is regenerated.
//
//------------------------------------------------------------------------------
partial class MyClass
{
[global::System.CodeDom.Compiler.GeneratedCodeAttribute("AutoConstructor", "5.0.0.0")]
public MyClass(global::MyDbContext context, global::System.Net.Http.IHttpClientFactory clientFactory, global::IService service, global::Microsoft.Extensions.Options.IOptions options)
{
this._context = context;
this._clientFactory = clientFactory;
this._service = service;
this._options = options?.Value;
}
}
```
A sample containing more cases is available at the end of this README.
## How to use
For any class where the generator will be used:
- Mark the class or struct as `partial`
- Use `AutoConstructorAttribute` on the class or struct
By default, all `readonly` non-`static` fields without initialization will be used. They will be injected with the same name without any leading `_`.
Fields marked with `AutoConstructorIgnoreAttribute` will be ignored.
Use `AutoConstructorInjectAttribute` to customize the behavior, usually when the injected parameter and the fields
do not have the same type. It takes three optional parameters:
- `initializer`: a string that will be used to initialize the field (by example `myService.GetData()`), default to the `parameterName` if null or empty.
- `parameterName`: the name of the parameter to used in the constructor (by example `myService`), default to the field name trimmed if null or empty.
- `injectedType`: the type of the parameter to used in the constructor (by example `IMyService`), default to the field type if null.
If no parameters are provided, the behavior will be the same as without the attribute. Using the attribute on a field that would not be injected otherwise
won't make the field injectable.
When using `AutoConstructorInjectAttribute`, the parameter name can be shared across multiple fields,
and even use a parameter from another field not annotated with `AutoConstructorInjectAttribute`, but type must match.
### Constructor accessibility
Constructor accessibility can be changed using the optional parameter `accessibility` on `AutoConstructorAttribute` (like `[AutoConstructor("internal")]`).
The default is `public` and it can be set to one of the following values:
- `public`
- `private`
- `protected`
- `internal`
- `protected internal`
- `private protected`
### Initializer method
It is possible to add a method call at the end of the constructor. To do this, the attribute `AutoConstructorInitializer` can be added to
a parameterless method that returns void. This will generate a call to the method at the end.
```csharp
[AutoConstructor]
internal partial class Test
{
private readonly int _t;
[AutoConstructorInitializer]
public void Initializer()
{
}
}
```
will generate
```csharp
public Test(int t)
{
this._t = t;
this.Initializer();
}
```
### Configuring `base` call
It is possible to configure which base constructor is called when a type has a non-object base type and has its constructor generated. By default, a call to `base` is emitted only when the is only one constructor on the base type.
This behavior can be changed by adding a `[AutoConstructorDefaultBase]` on a constructor in the base type to indicate that it must be chosen as the base call.
If the base type is also generated, the `addDefaultBaseAttribute` parameter on `AutoConstructorAttribute` can be used to generate the attribute with the generated constructor.
```csharp
internal class BaseClass
{
private readonly int _t;
[AutoConstructorDefaultBase]
public BaseClass(int t1, int t3)
{
this._t = t1 + t3;
}
public BaseClass(int t)
{
this._t = t;
}
public BaseClass()
{
}
}
[AutoConstructor]
internal partial class Test : BaseClass
{
private readonly int _t2;
}
```
will generate
```csharp
partial class Test
{
public Test(int t2, int t1, int t3) : base(t1, t3)
{
this._t2 = t2;
}
}
```
### Base constructor parameter matching
When inheriting a class, a call to the base constructor will be generated. By default, any parameter with the same name and the same type in both the parent and the
child class will be matched together.
```csharp
// This (same name and type)
public class ParentClass
{
private readonly int value;
public ParentClass(int value)
{
this.value = value;
}
}
[AutoConstructor]
public partial class Test : ParentClass
{
private readonly int value;
}
// Generates
partial class Test
{
public Test(int service) : base(service)
{
this.service = service;
}
}
// This (same name but not same type)
public class ParentClass
{
private readonly long value;
public ParentClass(long value)
{
this.value = value;
}
}
[AutoConstructor]
public partial class Test : ParentClass
{
private readonly int value;
}
// Generates
partial class Test
{
public Test(int service, long b0__service) : base(b0__service)
{
this.service = service;
}
}
```
If wanted, the matching on the type can be disable by setting the parameter `matchBaseParameterOnName` on `AutoConstructorAttribute` as `true`.
⚠️ This can lead to invalid code, since the type is no longer checked, anything can be used as a parameter with the same name. Use this only when necessary.
```csharp
// This (same name but not same type with matchBaseParameterOnName true)
public class ParentClass
{
private readonly long value;
public ParentClass(long value)
{
this.value = value;
}
}
[AutoConstructor(matchBaseParameterOnName: true)]
public partial class Test : ParentClass
{
private readonly int value;
}
// Generates
partial class Test
{
public Test(int service) : base(service)
{
this.service = service;
}
}
```
### Properties injection
Get-only properties (`public int Property { get; }`) are injected by the generator by default.
Non get-only properties (`public int Property { get; set;}`) are injected only if marked with (`[field: AutoConstructorInject]`) attribute.
The behavior of the injection can be modified using auto-implemented property field-targeted attributes on its backing field. The following code show an injected get-only property with a custom injecter:
```csharp
[field: AutoConstructorInject(initializer: "injected.ToString()", injectedType: typeof(int), parameterName: "injected")]
public int Property { get; }
```
⚠️ The compiler support for auto-implemented property field-targeted attributes is not perfect, and Roslyn analyzers are not running on backings fields so some warnings may not be reported.
## Configuration
### Generating `ArgumentNullException`
By default, null checks with `ArgumentNullException` are not generated when needed.
To enable this behavior, set `AutoConstructor_GenerateArgumentNullExceptionChecks` to `true` in the project file:
``` xml
true
```
5.2.X and previous versions
To enable this behavior, set `AutoConstructor_DisableNullChecking` to `false` in the project file.
### Generating `this()` calls
By default, if a non-generated parameterless constructor is available on the class (other than the implicit one), a call
to `this()` is generated with the generated constructor.
To disable this behavior, set `AutoConstructor_GenerateThisCalls` to `false` in the project file:
``` xml
false
```
This is also configurable at the attribute level with the `DisableThisCall` parameter on `AutoConstructorAttribute` (⚠ it is not possible force the generation at the attribute level if the generation is globally disabled).
### Generating XML documentation comment
By default, no XML documentation comment will be generated for the constructor.
To enable this behavior, set `AutoConstructor_GenerateConstructorDocumentation` to `true` in the project file:
``` xml
true
```
This will generate a default comment like this one, with each parameter reusing the corresponding field summary if available, and the parameter name otherwise:
``` c#
///
/// Initializes a new instance of the Test class.
///
/// Some field.
/// t2
```
By using the `AutoConstructor_ConstructorDocumentationComment` property, you can configure the comment message:
``` xml
Some comment for the {0} class.
```
This will generate the following code:
``` c#
///
/// Some comment for the Test class.
///
/// Some field.
/// t2
```
### Generating a parameterless constructor
If needed, a parameterless constructor can also be generated alongside the generated constructor using the `addParameterless` option on `AutoConstructor`.
``` csharp
[AutoConstructor(addParameterless: true)]
public partial class Test
{
public int Id { get; set; }
public string Name { get; set; }
}
```
will generate
```csharp
partial class Test
{
#pragma warning disable CS8618 // Non-nullable field must contain a non-null value when exiting constructor.
[global::System.ObsoleteAttribute("Not intended for direct usage.", true)]
public Test()
{
}
}
```
This option can also be used without any fields or properties to inject, this will disable the warning that will normally be reported and generate a parameterless constructor.
:warning: With inheritance, to be able to generate a parameterless constructor, the base type of the target type must have parameterless constructor itself.
By default, this constructor is marked as `[Obsolete]` with a default message. This is configurable with :
``` xml
false
Custom obsolete message
```
## Samples describing some cases
### Sample for fields
The following code
``` csharp
[AutoConstructor]
partial class Test
{
private readonly string _name;
// Won't be injected
private readonly Uri _uri = new Uri("/non-modified", UriKind.Relative);
// Won't be injected
[AutoConstructorIgnore]
private readonly DateTime _dateNotTaken;
// Won't be injected because not readonly. Attribute would be taken into account if this were a property, not a field.
[AutoConstructorInject]
private int _stuff;
// Won't be injected
private int? _toto;
// Support for nullables
private readonly DateTime? _date;
// Support for generics
private readonly List _items;
// Inject with custom initializer
[AutoConstructorInject("guid.ToString()", "guid", typeof(Guid))]
private readonly string _guidString;
// Use existing parameter defined with AutoConstructorInject
[AutoConstructorInject("guid.ToString().Length", "guid", typeof(Guid))]
private readonly int _guidLength;
// Use existing parameter from a basic injection
[AutoConstructorInject("name.ToUpper()", "name", typeof(string))]
private readonly string _nameShared;
}
```
will generate
```csharp
//------------------------------------------------------------------------------
//
// This code was generated by the AutoConstructor source generator.
//
// Changes to this file may cause incorrect behavior and will be lost if
// the code is regenerated.
//
//------------------------------------------------------------------------------
partial class Test
{
[global::System.CodeDom.Compiler.GeneratedCodeAttribute("AutoConstructor", "5.0.0.0")]
public Test(string name, global::System.DateTime? date, global::System.Collections.Generic.List items, global::System.Guid guid)
{
this._name = name ?? throw new global::System.ArgumentNullException(nameof(name));
this._date = date;
this._items = items ?? throw new global::System.ArgumentNullException(nameof(items));
this._guidString = guid.ToString() ?? throw new global::System.ArgumentNullException(nameof(guid));
this._guidLength = guid.ToString().Length;
this._nameShared = name.ToUpper() ?? throw new global::System.ArgumentNullException(nameof(name));
}
}
```
### Sample for get-only properties
The following code
``` csharp
[AutoConstructor]
public partial class Test
{
[field: AutoConstructorInject]
public int Injected { get; }
public int AlsoInjectedEvenWhenMissingAttribute { get; }
///
/// Some property.
///
[field: AutoConstructorInject]
public int InjectedWithDocumentation { get; }
[field: AutoConstructorInject]
public int InjectedBecauseExplicitInjection { get; set; }
[field: AutoConstructorInject]
public static int NotInjectedBecauseStatic { get; }
[field: AutoConstructorInject]
public int NotInjectedBecauseInitialized { get; } = 2;
[field: AutoConstructorIgnore]
public int NotInjectedBecauseHasIgnoreAttribute { get; }
[field: AutoConstructorInject(initializer: "injected.ToString()", injectedType: typeof(int), parameterName: "injected")]
public string InjectedWithoutCreatingAParam { get; }
}
```
will generate
```csharp
//------------------------------------------------------------------------------
//
// This code was generated by the AutoConstructor source generator.
//
// Changes to this file may cause incorrect behavior and will be lost if
// the code is regenerated.
//
//------------------------------------------------------------------------------
partial class Test
{
///
/// Initializes a new instance of the Test class.
///
/// injected
/// alsoInjectedEvenWhenMissingAttribute
/// Some property.
/// injectedBecauseExplicitInjection
[global::System.CodeDom.Compiler.GeneratedCodeAttribute("AutoConstructor", "5.0.0.0")]
public Test(int injected, int alsoInjectedEvenWhenMissingAttribute, int injectedWithDocumentation, int injectedBecauseExplicitInjection)
{
this.Injected = injected;
this.AlsoInjectedEvenWhenMissingAttribute = alsoInjectedEvenWhenMissingAttribute;
this.InjectedWithDocumentation = injectedWithDocumentation;
this.InjectedBecauseExplicitInjection = injectedBecauseExplicitInjection;
this.InjectedWithoutCreatingAParam = injected.ToString() ?? throw new global::System.ArgumentNullException(nameof(injected));
}
}
```
## Diagnostics
### ACONS01
The `AutoConstructor` attribute is used on a class that is not partial.
### ACONS02
The `AutoConstructor` attribute is used on a class without fields to inject (without specifying `addParameterless` as true).
### ACONS03
The `AutoConstructorIgnore` attribute is used on a field that won't already be processed.
### ACONS04
The `AutoConstructorInject` attribute is used on a field that won't already be processed.
### ACONS05
The `AutoConstructorIgnore` or `AutoConstructorInject` are used on a class without the `AutoConstructor` attribute.
### ACONS06
A type specified in `AutoConstructorInject` attribute does not match the type of another parameter with the same name.
In the following sample, both fields will be injected with `guid` as parameter name, but one of type `string` and the other of type `Guid`,
preventing the generator from running.
``` csharp
public partial class Test
{
[AutoConstructorInject("guid.ToString()", "guid", typeof(Guid))]
private readonly string _guid2;
private readonly string _guid;
}
```
### ACONS07
The accessibility defined in the `AutoConstructor` attribute is not an allowed value.
### ACONS08
`AutoConstructorInitializer` attribute used on multiple methods inside type.
### ACONS09
`AutoConstructorInitializer` attribute used on a method not returning void.
### ACONS10
`AutoConstructorInitializer` attribute used on a method with parameters.
### ACONS11
`AutoConstructorDefaultBase` attribute used on multiple constructors inside type.
### ACONS12
The `addParameterless` option is used on a type whose base type does not have a parameterless constructor.
### ACONS99
`AutoConstructor_DisableNullChecking` is obsolete.