Working with Variables

The Variable class in LamarCodeGeneration models the CLR type and usage of a value within a generated method.

Here are some samples of creating variable objects with a variable type and name:

// Create a connection for the type SqlConnection 
// with the name "conn"
var conn = Variable.For<SqlConnection>("conn");

// Pretty well the same thing above
var conn2 = new Variable(typeof(SqlConnection), "conn2");

// Create a variable with the default name
// for the type
var conn3 = Variable.For<SqlConnection>();
conn3.Usage.ShouldBe("sqlConnection");

Default Naming

If you do not give a name for a variable, Lamar will derive a default variable name from the type like this:

var widget = Variable.For<IWidget>();
widget.Usage.ShouldBe("widget");

The best way to understand the full rules for deriving the default variable names is to just peek at the unit tests within the Lamar codebase.

Creator Frame

If a variable is created by a Frame, you really want to mark that relationship by either passing the creating frame into the constructor function like this:

public class NowFetchFrame : SyncFrame
{
    public NowFetchFrame(Type variableType)
    {
        // Notice how "this" frame is passed into the variable
        // class constructor as the creator
        Variable = new Variable(variableType, "now", this);
    }
    
    public Variable Variable { get; }
    
    public override void GenerateCode(GeneratedMethod method, ISourceWriter writer)
    {
        writer.WriteLine($"var {Variable.Usage} = {Variable.VariableType.FullName}.{nameof(DateTime.UtcNow)};");
        Next?.GenerateCode(method, writer);
    }
}

Overriding Variable Usage or Type

Do this sparingly, but you can override the name or usage and type of a previously built variable like this:

var service = new Variable(typeof(IService), "service");
service.OverrideName("myService");
service.OverrideType(typeof(WhateverService));

Derived Variables

Variables don't have to mean literal C# variables in the generated code. They can be derived values like this example:

var now = new Variable(typeof(DateTime), $"{typeof(DateTime).FullName}.{nameof(DateTime.Now)}");

Dependencies to Other Variables

For the sake of frame ordering, you might need to give Lamar a hint that your variable depends on another variable. Here's an example of doing that with the HttpResponse type from ASP.Net Core:

var context = Variable.For<HttpContext>();
var response = new Variable(typeof(HttpResponse), $"{context.Usage}.{nameof(HttpContext.Response)}");
response.Dependencies.Add(context);

Working with Variables #

Default Naming #

Creator Frame #

Overriding Variable Usage or Type #

Derived Variables #