bjhasem.blogg.se - Ruby code blocks

See “Syntax” section above for more information. block_name Ruby Type: String | Default Value: The resource block's name

The ruby_block resource has the following properties: block Ruby Type: BlockĪ block of Ruby code. Or is queued up to run at the end of a Chef Infra Client run.

Once notified, this resource block either runs immediately :nothing This resource block does not act unless notified by another resource to The ruby_block resource has the following actions: :create The same as :run. See “Properties” section below for more information about all of the properties that may be used with this resource.

block and block_name are properties of this resource, with the Ruby type shown.

action identifies which steps Chef Infra Client will take to bring the node into the desired state.

block is the block of Ruby code to be executed.

name is the name given to the resource block.

In other words, executing something under the context of a binding object is the same as if that code was in the same place where that binding was defined (remember the ‘anchor’ metaphor).Block_name String # defaults to 'name' if not specifiedĪction Symbol # defaults to :run if not specified end # The reason is that foo was never defined outside of the method. In this post we’ll discuss what a block is. Blocks are also an integral part of many domain-specific languages (DSLs) in libraries like RSpec, Factory Bot, and Rails itself. # If you try to print foo directly you will get an error. Blocks are a fundamental concept in Ruby. # even though we are outside of the method # Foo is available thanks to the binding, When you create a Binding object via the binding method, you are creating an ‘anchor’ to this point in the code.Įvery variable, method & class defined at this point will be available later via this object, even if you are in a completely different scope. Code blocks allow multiple lines of code to be written. The code between the keywords is what gets executed.

Blocks are defined by the starting and ending keywords, ' do ' and ' end ', respectively. Where do Ruby procs & lambdas store this scope information? Code Blocks Code blocks provide structure for executable statements in Ruby. This happens because the proc is using the value of count from the place where the proc was defined, and that’s outside of the method definition. It would seem like 500 is the most logical conclusion, but because of the ‘closure’ effect this will print 1. What do you think this program will print? So we can call mymethod and pass it the above block. After the block runs, control returns to the method that invoked it. When the block is called from the method, the code in the block body will be executed. We also have a proc named my_proc, and a call_proc method which runs (via the call method) any proc or lambda that is passed in as an argument. The block body consists of one or more lines of Ruby code between do and end. In this example we have a local count variable, which is set to 1. P call_proc(my_proc) # What does this print? They don’t carry the actual values, but a reference to them, so if the variables change after the proc is created, the proc will always have the latest version.

Ruby Yield Keyword What does yield mean in Ruby Yield is a Ruby keyword that calls a block when you use it. This could be something like writing data to a file, comparing if one element is equal to another, or even printing an error message. This concept, which is sometimes called closure, means that a proc will carry with it values like local variables and methods from the context where it was defined. Ruby’s closure-like constructs (blocks, procs and lambdas) are neat and super useful, but many developers initially misunderstand what exactly return means in a Proc. A Ruby block is useful because it allows you to save a bit of logic (code) & use it later. When you create a Ruby proc, it captures the current execution scope with it. Ruby procs & lambdas also have another special attribute. Taking a look at this list, we can see that lambdas are a lot closer to a regular method than procs are. Procs don’t care about the correct number of arguments, while lambdas will raise an exception.Procs return from the current method, while lambdas return from the lambda itself.Ruby blocks are little anonymous functions that can be passed into methods.īlocks are enclosed in a do / end statement or between brackets.