String.Format: Allow variables for specifying the alignment component

[robertmclaws]

When formatting a string in C#, you can specify an alignment parameter by adding a comma and then specifying either a positive or negative number.

The problem is that this number must be a constant, which makes it very difficult to format large sections of data where you don't know the length.

To demonstrate a real-world situation, let's consider the need to output the contents of a DependencyInjection container to a text file for unit testing.

ServiceType: Microsoft.Restier.Core.Routing.RestierApiRouteDictionary, ImplementationType: Microsoft.Restier.Core.Routing.RestierApiRouteDictionary, Lifetime: Singleton
ServiceType: Microsoft.Restier.Core.Query.DefaultQueryExecutor, ImplementationType: Microsoft.Restier.Core.Query.DefaultQueryExecutor, Lifetime: Transient
ServiceType: Microsoft.Restier.Core.Query.IQueryExecutor, ImplementationType: , Lifetime: Singleton
ServiceType: Microsoft.Extensions.DependencyInjection.ApiServiceContributor`1[Microsoft.Restier.Core.Query.IQueryExecutor], ImplementationType: , Lifetime: Singleton
ServiceType: Microsoft.Restier.Core.PropertyBag, ImplementationType: Microsoft.Restier.Core.PropertyBag, Lifetime: Scoped
ServiceType: Microsoft.Restier.Core.Submit.IChangeSetItemAuthorizer, ImplementationType: , Lifetime: Singleton
ServiceType: Microsoft.Extensions.DependencyInjection.ApiServiceContributor`1[Microsoft.Restier.Core.Submit.IChangeSetItemAuthorizer], ImplementationType: , Lifetime: Singleton
ServiceType: Microsoft.Restier.Core.Submit.IChangeSetItemFilter, ImplementationType: , Lifetime: Singleton

That's kind of a pain in the butt to read. What I really want is for it to look like this:

Lifetime: Singleton  |  ServiceType: Microsoft.OData.Json.IJsonReaderFactory                                         |  ImplementationType: Microsoft.OData.Json.DefaultJsonReaderFactory  |  ImplementationFactory: None
Lifetime: Singleton  |  ServiceType: Microsoft.OData.Json.IJsonWriterFactory                                         |  ImplementationType: None                                           |  ImplementationFactory: value(CloudNimble.Breakdance.Assemblies.DependencyInjectionTestHelpers+<>c__DisplayClass3_0).func
Lifetime: Singleton  |  ServiceType: Microsoft.OData.ODataMediaTypeResolver                                          |  ImplementationType: None                                           |  ImplementationFactory: value(CloudNimble.Breakdance.Assemblies.DependencyInjectionTestHelpers+<>c__DisplayClass3_0).func
Lifetime: Scoped     |  ServiceType: Microsoft.OData.ODataMessageInfo                                                |  ImplementationType: Microsoft.OData.ODataMessageInfo               |  ImplementationFactory: None
Lifetime: Singleton  |  ServiceType: Microsoft.OData.ServicePrototype`1[Microsoft.OData.ODataMessageReaderSettings]  |  ImplementationType: None                                           |  ImplementationFactory: value(CloudNimble.Breakdance.Assemblies.DependencyInjectionTestHelpers+<>c__DisplayClass3_0).func
Lifetime: Scoped     |  ServiceType: Microsoft.OData.ODataMessageReaderSettings                                      |  ImplementationType: None                                           |  ImplementationFactory: value(CloudNimble.Breakdance.Assemblies.DependencyInjectionTestHelpers+<>c__DisplayClass3_0).func
Lifetime: Singleton  |  ServiceType: Microsoft.OData.ServicePrototype`1[Microsoft.OData.ODataMessageWriterSettings]  |  ImplementationType: None                                           |  ImplementationFactory: value(CloudNimble.Breakdance.Assemblies.DependencyInjectionTestHelpers+<>c__DisplayClass3_0).func
Lifetime: Scoped     |  ServiceType: Microsoft.OData.ODataMessageWriterSettings                                      |  ImplementationType: None                                           |  ImplementationFactory: value(CloudNimble.Breakdance.Assemblies.DependencyInjectionTestHelpers+<>c__DisplayClass3_0).func

Consider this code that outputs the contents of a IServiceCollection to a string, which should work: (the AppendLine inside the ForEach)

    private static string ToDetailedString(this List<ServiceDescriptor> list)
    {
        if (list == null || !list.Any())
        {
            return string.Empty;
        }

        //RWM: Get the length of each item, sort longest to shortest, grab the first one.
        var serviceTypeLength = list.Select(c => c.ServiceType.ToString().Length).OrderByDescending(c => c).First();
        var implementationTypeLength = list.Select(c => c.ImplementationType?.ToString()?.Length ?? 0).OrderByDescending(c => c).First();

        var sb = new StringBuilder();

        list.ForEach(c =>
        {
            sb.AppendLine($"Lifetime: {c.Lifetime,-9}  |  ServiceType: {c.ServiceType,-serviceTypeLength}  |  ImplementationType: {c.ImplementationType,-implementationTypeLength}  |  ImplementationFactory: {c.ImplementationFactory}");
        });
        return sb.ToString();
    }

But for some reason, this is not possible. This forces us to have to include a function to generate the string format, which makes the code considerably more complicated:

    private static string ToDetailedString(this List<ServiceDescriptor> list)
    {
        if (list == null || !list.Any())
        {
            return string.Empty;
        }

        //RWM: Get the length of each item, sort longest to shortest, grab the first one.
        var serviceTypeLength = list.Select(c => c.ServiceType.ToString().Length).OrderByDescending(c => c).First();
        var implementationTypeLength = list.Select(c => c.ImplementationType?.ToString()?.Length ?? 0).OrderByDescending(c => c).First();

        var sb = new StringBuilder();

        list.ForEach(c =>
        {
            sb.Append($"Lifetime: {c.Lifetime,-9}  |  ServiceType: ");
            sb.AppendFormat(GetFormatString(0, -serviceTypeLength), c.ServiceType.ToString());
            sb.Append("  |  ImplementationType: ");
            sb.AppendFormat(GetFormatString(0, -implementationTypeLength), c.ImplementationType?.ToString() ?? "None");
            sb.Append($"  |  ImplementationFactory: {FuncToString(c.ImplementationFactory)}\n");
        });
        return sb.ToString();
    }

    private static string GetFormatString(int index, int spacing)
    {
        var test = $"{{{index}, {spacing}}}";
        return test;
    }

There has to be a way to allow that parameter to be a variable. Any chance we could make it happen? Thanks so much for your consideration!

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[robertmclaws]

@danmoseley Question for you: out of curiosity, what was the rationale behind moving this to the discussions section? It was not meant to be a question, but a feature request for .NET 6.0.

Thanks!