Extension method doesn't work (Quick Graph Serialization)

Question

Error: The type arguments for method GraphMLExtensions.SerializeToGraphML<TVertex, TEdge, TGraph>(TGraph, XmlWriter) cannot be inferred from the usage.

using System.Xml;
using QuickGraph;
using QuickGraph.Serialization;    

var g = new AdjacencyGraph<string, Edge<string>>();

.... add some vertices and edges ....

using (var xwriter = XmlWriter.Create("somefile.xml"))
  g.SerializeToGraphML(xwriter);

The code is copied from QuickGraph's documentation. However when I write it explicitly it works:

using (var xwriter = XmlWriter.Create("somefile.xml"))
   GraphMLExtensions.SerializeToGraphML<string, Edge<string>, AdjacencyGraph<string, Edge<string>>>(g, xwriter);

Edit: I saw some related questions, but they are too advanced for me. I'm just concerned about using it. Am I doing something wrong or it's the documentation?

Do you have all assemblies referenced and all needed usings? — BendEg, Dec 02 '15 at 07:56
Yes. As you can see from the second code GraphMLExtensions class is recognized. It's in the QuickGraph.Serialization namespace. — kptlronyttcna, Dec 02 '15 at 07:57
What happens, if you set the generic types? `g.SerializeToGraphML<..., ...>(xwriter);`? — BendEg, Dec 02 '15 at 08:00
It works. But Intellisense doesn't show SerializeToGraphML method. — kptlronyttcna, Dec 02 '15 at 08:02

Yuval Itzchakov · Accepted Answer · 2017-05-01T14:17:38.067

5

Am I doing something wrong or it's the documentation?

The problem isn't with the extension method. The problems lays in the fact that when you use the full static method path, you're suppling the generic type arguments explicitly, while using the extension method you're not supplying any at all.

The actual error is related to the fact that compiler can't infer all the generic type arguments for you, and needs your help by explicitly passing them.

This will work:

using (var xwriter = XmlWriter.Create("somefile.xml"))
{
    g.SerializeToGraphML<string, Edge<string>, 
         AdjacencyGraph<string, Edge<string>>>(xwriter);
}

edited May 01 '17 at 14:17

answered Dec 02 '15 at 08:02

Yuval Itzchakov

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@kptlronyttcna You welcome. Perhaps the compiler is able to infer *some* of the type arguments for you. I'm not sure which, try combinations yourself. – Yuval Itzchakov Dec 02 '15 at 08:11

score 2 · Answer 2 · answered Dec 02 '15 at 08:04

The biggest hint here is that you're having to be explicit for the type parameters in your GraphMLExtensions.SerializeToGraphML() call.

I took a quick look at the source for this, and realized what's up.

You are using this overload:

public static void SerializeToGraphML<TVertex, TEdge, TGraph>(
    this TGraph graph,
         XmlWriter writer)
         where TEdge : IEdge<TVertex>
         where TGraph : IEdgeListGraph<TVertex, TEdge>

Here TEdge and TGraph need to be set to specific types, but there are no arguments that match the type parameters. This means you have to explicitly set them.

score 2 · Answer 3 · answered Dec 02 '15 at 08:05

2

You need to specify the generic types, so that the correct generic method will be used. Just add them for calling the generic method:

// Your using block, ...
g.SerializeToGraphML<string, Edge<string>, AdjacencyGraph<string, Edge<string>>>(xwriter);

answered Dec 02 '15 at 08:05

BendEg

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Extension method doesn't work (Quick Graph Serialization)

3 Answers3