C#•2y ago

❔ What is the use of datatype after function name?

I have a function signature that looks like this:

c#
        public static IServiceCollection AddMongoRepository<T>(this IServiceCollection services, string collectionName) where T : IEntity

c#
        public static IServiceCollection AddMongoRepository<T>(this IServiceCollection services, string collectionName) where T : IEntity

What is the use of <T> after the function name?

10 Replies

Thinker•2y ago

That's a type parameter It essentially lets you pass a type as a parameter to a function

Thinker•2y ago

https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/generics/generic-methods

Generic Methods - C# Programming Guide

Learn about methods declared with type parameters, known as generic methods. See code examples and view additional available resources.

Thinker•2y ago

T in this case is constrained to implementing the IEntity interface. I.e. when you call AddMongoRespository, the type you specify in the <> has to implement IEntity.

shivam51OP•2y ago

This function is actually a part of generic service, one of the lines inside the function is :

            services.AddSingleton<IRepository<T>>(provider =>

            services.AddSingleton<IRepository<T>>(provider =>

So if I need to use <T> anywhere inside the function its important to pass a type parameter while function call?

        public static IServiceCollection AddMongoRepository<T>(this IServiceCollection services, string collectionName) where T : IEntity
        {
            services.AddSingleton<IRepository<T>>(provider =>
            {
                var database = provider.GetService<IMongoDatabase>();
                return new MongoRepository<T>(database, collectionName);
            });
            return services;
        }

        public static IServiceCollection AddMongoRepository<T>(this IServiceCollection services, string collectionName) where T : IEntity
        {
            services.AddSingleton<IRepository<T>>(provider =>
            {
                var database = provider.GetService<IMongoDatabase>();
                return new MongoRepository<T>(database, collectionName);
            });
            return services;
        }

        public static IServiceCollection AddMongoRepository(this IServiceCollection services, string collectionName)
        {
            services.AddSingleton<IRepository<IEntity>(provider =>
            {
                var database = provider.GetService<IMongoDatabase>();
                return new MongoRepository<IEntity>(database, collectionName);
            });
            return services;
        }

        public static IServiceCollection AddMongoRepository(this IServiceCollection services, string collectionName)
        {
            services.AddSingleton<IRepository<IEntity>(provider =>
            {
                var database = provider.GetService<IMongoDatabase>();
                return new MongoRepository<IEntity>(database, collectionName);
            });
            return services;
        }

so both of these functions are right. Is this correct understanding?

Thinker•2y ago

The second one adds an IRepository of specifically IEntity. The first adds an IRepository of a specific type (which still implements IEntity).

shivam51OP•2y ago

so both are correct syntax right? so in the second case I could simply call the function without specifuying the type in <>

Thinker•2y ago

In the second one, if you call services.GetService<IRepository<SomeEntity>>() then it'll throw an exception. It'll only work if you do services.GetService<IRepository<IEntity>>()

shivam51OP•2y ago

yes, that makes sense.

Thinker•2y ago

Since I assume the point of IRepository is to contain entities of a specific type, the first one is correct.

Accord•2y ago

Looks like nothing has happened here. I will mark this as stale and this post will be archived until there is new activity.

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❔ What is the use of datatype after function name?