https://github.com/andrej-dyck/dotnet-extensions-require
📦 Require Expressions - A pre-condition checks library for .Net via extensions methods on types.
https://github.com/andrej-dyck/dotnet-extensions-require
argument-checks code-contracts csharp dotnet extension-methods guard nuget-package preconditions require
Last synced: 4 months ago
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📦 Require Expressions - A pre-condition checks library for .Net via extensions methods on types.
- Host: GitHub
- URL: https://github.com/andrej-dyck/dotnet-extensions-require
- Owner: andrej-dyck
- License: mit
- Created: 2022-05-17T17:45:08.000Z (about 4 years ago)
- Default Branch: main
- Last Pushed: 2022-11-11T14:23:30.000Z (over 3 years ago)
- Last Synced: 2025-11-09T03:25:26.171Z (6 months ago)
- Topics: argument-checks, code-contracts, csharp, dotnet, extension-methods, guard, nuget-package, preconditions, require
- Language: C#
- Homepage:
- Size: 35.2 KB
- Stars: 2
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
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README
# Require Expressions for .Net
[](https://codecov.io/gh/andrej-dyck/dotnet-extensions-require)
[](https://www.nuget.org/packages/Require-Expressions/)
A small library that provides _pre-condition_ checks as an extension method on types.
This allows the client code to check a condition on arguments and use the value directly if no exception is thrown.
```csharp
Reservation Request(DateTime now, DateTime reservationDate, int seats) =>
new Reservation(
reservationDate.Require(d => d > now, d => $"Reservation date {d} must be in the future"),
seats.Require(seats > 0, () => "Expected positive number of seats")
);
```
## NuGet Package
```shell
dotnet add package Require-Expressions
```
## Examples for `Require`
Basic `Require` function
```csharp
var requestedSeats = seats.Require(condition: seats > 0);
// throws ArgumentException with "expected: seats > 0" as message when condition is not met
var requestedSeats = seats.Require(
condition: seats > 0,
expectation: "Expected positive number of seats" // or with custom expectation message
);
```
`Require` functions with lazily constructed expectation messages
```csharp
var requestedSeats = seats.Require(
condition: seats > 0,
expectation: () => "Expected positive number of seats"
);
var requestedDate = reservationDate.Require(
condition: reservationDate > now,
expectation: d => $"Reservation date {d} must be in the future"
);
```
`Require` functions with predicate for convenience
```csharp
var requestedSeats = seats.Require(condition: s => s > 0);
// throws ArgumentException with "expected: s => s > 0" as message when condition is not met
var requestedSeats = seats.Require(
condition: s => s > 0,
expectation: "Expected positive number of seats" // or with custom expectation message
);
var requestedDate = reservationDate.Require(
requirement: d => d > now,
expectation: d => $"Reservation date {d} must be in the future"
);
```
## Examples for `Check`
For checks other than on arguments, the `Check` function can be used
```csharp
var reservationRequest = JsonSerializer.Deserialize(request)
.Check(requirement: r => r.Seats > 0) // expectation message will be "expected r => r.Seats > 0"
.Check(r => r.Date > now, r => $"Reservation date {r.Date} must be in the future")
// throws CheckFailed with expectation as message when requirement is not satisfied
```
With `Check`, custom exceptions can be constructed
```csharp
var reservationRequest = JsonSerializer.Deserialize(request)
.Check(r => r.Seats > 0, exception: () => new SeatsMustBePositive())
.Check(r => r.Date > now, exception: r => new MustBeFutureDateReservateion(r.Date))
```
## Q&A
**Why yet another preconditions library?**
Most libraries I found use precondition _statements_, while I found preconditions as _expressions_ more useful.
For example, the latter allows for [_expression-bodied_ functions](
https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/statements-expressions-operators/expression-bodied-members
).
**I don't like extension methods**
No problem, there are many other great precondition libraries. Have a look
at [.Net's contracts](https://docs.microsoft.com/en-us/dotnet/api/system.diagnostics.contracts?view=net-6.0).
**I don't want yet another dependency**
No problem, just copy&paste the code you need into your project. Or use the build-in .Net contracts.
**Can you add this function too?**
Probably not as I want to keep this library small and focused. But you are very welcome to post a PR.
## Build & Test
**Build project**
```shell
dotnet build
```
**Run unit tests**
```shell
dotnet test
```