CODEWITHSUNDEEP
c#.netvisual-studioazure-functions
James Wood
James Wood

Reputation: 17562

How does one function result in multiple functions?

I'm currently working with Azure Functions and I just found this interface definition.

Assembly Microsoft.Extensions.Logging.Abstractions, Version=1.1.1.0, Culture=neutral, PublicKeyToken=adb9793829ddae60

using System;

namespace Microsoft.Extensions.Logging
{
    public interface ILogger
    {
        IDisposable BeginScope<TState>(TState state);

        bool IsEnabled(LogLevel logLevel);

        void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Exception exception, Func<TState, Exception, string> formatter);
    }
}

I am particular interested in void Log<TState>. This function has what looks like a generic, but seems to magically expand into 6 functions.

log.LogCritical("...");
log.LogDebug("...");
log.LogError("...");
log.LogInformation("...");
log.LogTrace("...");
log.LogWarning("...");

I receive the reference to log via the Azure Function defintion.

[FunctionName("WhoAmI")]
public static async Task<HttpResponseMessage> Run([HttpTrigger(AuthorizationLevel.Function, "get", "post", Route = null)] HttpRequestMessage req, ILogger log)
{ ... }

The Microsoft samples and documentation reflect this.

I'm guessing this is a C# or Visual Studio feature and not witchcraft, but which feature is it?

Upvotes: 0

Views: 110

Answers (1)

Mikhail Shilkov
Mikhail Shilkov

Reputation: 35134

This is C# feature called Extension Methods. These methods are defined in LoggerExtensions static class. Here is a sample signature:

public static void LogDebug (
    this ILogger logger, EventId eventId, string message, object[] args);

It's the keyword this which makes the call look like it's the member of interface.

LoggerExtensions class.

C# Extension methods.

Credits to @SirRufo for giving the right hint in the comments. I just don't want to leave this question without the full answer :)

Upvotes: 4

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