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View Code? Open in Web Editor NEWA spike project to demonstrate some design patterns
A spike project to demonstrate some design patterns
This project is designed to demonstrate some design patterns including: -Decorator -Dependency Injection -Builder -Progressive Builder -Conditional Builder
I've come across your question related to this on StackOverflow a couple times, and also came to your site.
I know this is quite old, but I have some issues with ConditionalBuilder. And maybe they're just me.
First of all, I like the builderActions list. In fact, I have started doing that with all my Fluent Builders, as it saves the actual object creation to the end, when Build() is called. That seems cleaner to me.
However, I don't like the way the ConditionalBuilder grabs the last action from the list. Seeing the array indexer of Length - 1 makes me shudder. :)
I also don't like the way that conditions can be applied to anything. It seems like to me that you want to limit which items can have conditions. Although perhaps I am wrong here. But if you do want it to apply to all, then it seems like to me I should be able to do something like the following:
var ninjaBuilder = NinjaBuilder
.CreateNinjaBuilder()
.AtLevel(level)
.WithShurikens(10)
.WithSkill("hideinshadows")
.When(() => level > 5)
.When(() => SubClass == NinjaSubClass.Shadow)
And of course, this would fail, because if the first condition failed, then my second condition would now be applied to WithShurikens, not WithSkill.
So, I suggest the following changes.
First, add a new class, ConditionBuilder:
public class ConditionBuilder<T, TBuilder> where T : class where TBuilder : IFluentBuilder<T>
{
private readonly TBuilder builder;
private readonly Action<T> action;
public ConditionBuilder(TBuilder builder, Action<T> action)
{
this.builder = builder;
this.action = action;
}
public TBuilder When(Func<T, bool> condition)
{
builder.BuilderActions.Add(ba =>
{
if (condition(ba))
action(ba);
});
return builder;
}
public TBuilder AsBuilder()
{
return builder;
}
}
IFluentBuilder is defined as follows:
public interface IFluentBuilder<T> where T : class
{
List<Action<T>> BuilderActions { get; set; }
T Build();
}
Then we make the following changes to your existing code.
public class NinjaBuilder
{
private readonly List<Action<Ninja>> _builderActions;
becomes
public class NinjaBuilder : IFluentBuilder<Ninja>
{
public List<Action<Ninja>> BuilderActions { get; set; } = new List<Action<Ninja>>();
obviously references to _builderActions would change too.
And finally, we change WithSkill from
public NinjaBuilder WithSkill(string skill)
{
_builderActions.Add(s => s.Skill = skill);
return this;
}
to
public ConditionBuilder<Ninja, NinjaBuilder> WithSkill(string skill)
{
return new ConditionBuilder<Ninja, NinjaBuilder>(this, s => s.Skill = skill);
}
Note, that this doesn't totally solve my issue above about multiple .When conditions. Well, it does, because they aren't allowed now. :) But if you actually wanted multiple .When's you'd have to do a bit more work.
But now only the WithSkill method can have conditions, because it's the only one that returns a ConditionalBuilder
This seems cleaner to me. And we never actually remove actions from our list. Instead, we actually make a conditional action. Which is kind of what I would expect from looking at how the methods are used.
There is one thing I still don't like. The AsBuilder method in ConditionalBuilder. If you use the WithSkill, but don't supply a condition, then you now have a ConditionalBuilder<Ninja, NinjaBuilder> object, rather than a NinjaBuilder object. So, your next .With or .Build will generate a compile time error. The AsBuilder method fixes that, but now feels a bit clunky:
var ninjaBuilder = NinjaBuilder
.CreateNinjaBuilder()
.AtLevel(level)
.WithShurikens(10)
.WithSkill("hideinshadows")
.AsBuilder()
.Build();
Of course, you could get around that by supplying a When condition such as .When(() => true)
, but that also seems clunky.
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