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As in java8:
someList.stream().map(e->e.getXXX()).toList()
For example, I have a Student array/slice, and the struct Student contains properties like Id, Name, and so on.
I want to extract all Ids into a NEW array/slice with one-line code like java8 as mentioned above, instead of range. Is there is an example?
Currently there is not an easy, builtin way to do this. Although Go has first-class functions and lexical closure, it's not possible to write a function like map that will operate on arbitrary types in the way you want. (Also, there's no compact lambda syntax, but I consider that a relatively minor issue).
Instead, you have to do one of the following:
Operate on interface{}. While this would let you write a func map([]interface{}, func(interface{})interface{}) []interface{}, you lose compile-time type safety, you lose performance, and a []interface{} is not a []string (or whatever the type is of the field you wanted to fetch), nor can you even type-assert it to one, so working with the result is cumbersome.
Use code-generation. There are libraries out there that will generate map/filter/etc. code for you, specialized to given types, so that none of the disadvantages of #1 apply. And Go ships with a Go parser in the standard library, so most code generators are fairly robust. But code generation is a separate build step, hampers debuggability, and can hurt the clarity of code.
Just live with boilerplate, writing lots of loops, and forget about trying to achieve functional style.
Wait for Go 1.18 to bring generics, which should make libraries of functional idioms a lot more practical.
Most experienced Go users would recommend approach #3, and so do I (reluctantly).
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In OCaml, there is a construct called univ_map.t, which allows you to map from 'a Type_equal.Id.t values to 'as. Here is an example.
Is there a construct that would allow me to do something similar in Rust? I know in OCaml they are implemented with open variants, which I don't believe Rust has.
I'm not familiar with OCaml, but looking at the docs:
Univ_map: Universal/heterogeneous maps [...] useful for storing values of arbitrary type in a single map [...] built on top of Univ.
Univ: An extensible universal variant type. Every type id corresponds to one branch of the variant type.
The closest thing that Rust has that sounds like Univ is the Any trait, which is designed to represent any type (with exceptions). However, there is no standard type for storing a collection of Anys that is accessed by its TypeId. From looking how popular crates handle this, its usually a bespoke wrapper around HashMap<TypeId, Box<dyn Any>> or similar. I hope I've understood correctly.
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In some Golang Tips said that: small object should pass by value and big object should pass by reference.
But how big object is small object?
If a struct has 10+ Fields. should it pass by value?
As you see from the discussion it is "hard" to understand when to use a pointer or a reference. If you are learning the Golang I suggest to use this approach to decide when to use pointer or reference:
I need to use a struct only for read purpose
In this case I suggest to use a pointer to a struct, that's for performance reason (copy a struct is a time consuming operation as you can tell, no matter if is a "big" struct or a small one).
I need to use a struct on multiple function each one write something on the struct but the various function should be no influence each other
In this case you should pass the struct as reference.
I need to use a struct on multiple function each one write something on the struct and the various function should be use the result of previous function
In this case you should pass the struct by pointer.
As you can see this approach avoids to think about the "dimension" of the struct and focus on the use of the struct, I think this is a better approach because is not always easy to define the dimension of a struct.
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In furthering my study of Ruby, I've noticed that some methods really seem to give power to the language, while others are just syntactic sugar.
Examples of sugar: .split, .strip, i.e. any methods that just make doing a menial task with a data structure easier.
Examples of power methods: call, send, responds_to?, method_missing, etc.
It seems like if you understand those "power methods" you really know the language.
Curious about three things:
Has anyone every made such a distinction, be it in a book/blog post etc?
Do you personally make such a distinction?
If you feel what I'm saying is correct, what "power methods" should I know and use better?
Thanks (hope this question doesn't get closed!)
These aren't really "power methods" but are just another tool in the toolbox that is the Ruby library.
Methods like call and send are for low-level operations, bypassing the usual Ruby semantic layer. responds_to? is often used when writing generic code that uses duck typing, and method_missing is a way of writing code that responds to a variety of methods in a dynamic way. This is how Rails ActiveRecord handles methods calls like find_by_name_or_phone automatically.
Methods like split, strip and chomp are simply data transformation methods. Their primary function is to convert one thing into another, optionally in-place.
I don't think there's a distinction between any of these methods, they're all quite useful, but they do have their particular uses. As far as Ruby is concerned, though, all methods are equal, there's no hierarchy or inherent importance to them.
Some methods you will use very infrequently, so you're less likely to ever have need for them unless you've done a lot of Ruby.
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What do you think fellow programmers about using short functions vs using inline code?
Example with function:
//Check if all keys from $keys exist in $array
function functionName(array $array, array $keys) {
return array_diff($keys, array_keys($array));
}
functionName($mas,$keys);
vs. using just the code:
array_diff($keys, array_keys($mas));
I think that in your example, it's superfluous. There's no need to create an extra function call and add bytes to the filesize without good reason.
Also, the inline array_diff($keys, array_keys($mas)); is a lot easier to debug for fellow programmers, than looking through your code to find out exactly what functionName() does and where it is located.
It depends on what functionName actually is.
If you're using customerDetailsAreValid throughout your code and you suddenly have to add validation of $array['email'], you're going to be grateful for the separation of intent and implementation.
If on the other hand you're wrapping array_diff in the function diffArray there isn't much point.
I think clarity is a prime concern when writing logic you hope will be around for any amount of time.
In general, I abhor inline functions. I think they are lazy, promote spaghetti code, and in general exude a complete lack of concern for style/readability/clarity on the part of the developer.
Filesize - I find this argument very arbitrary. The js files are transmitted once and then cahced. In many cases, you find descriptive names, etc, (hopefully comments) that all add to file size. If size is very important , use a file minimizer that makes a file as tiny as possible.
Looking for a function? How about trying to figure out exactly what is going on in a voluminous docReady. CTL-F usually invokes a find facility.
I will grant that there can be simple cases where an inline function detracts little from the readability of the code. However, the inline approach will never be MORE CLEAR than the alternate separation of reference and implementation.
my two cents
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I'd like to write a code beautifier and i thought of using Ruby to do it. Could someone show me a place to get started? I've seen a lot of code beautifiers online but I've never come across any tutorials on how to write one. Is this a very challenging task for someone who's never undertaken any projects such as writing a compiler, parser, etc. before?
(Is there another langauge which would be more well suited for this kind of task, excluding C/C++?)
Python has an interesting feature - it exposes its own parser to scripts. There are examples that use the AST - abstract syntax tree - and do the pretty printing.
I'm not aware that Ruby exposes its own parser to its scripts in such a way, but there are parsers for Ruby written in Ruby here.
Well... I think the initial steps are what you'd do for any project.
Write a list of requirements.
Describe a user interface to your program, that you like and won't prevent you meeting those requirements.
Now you can write down more of a "code" design, and pick the language that would be easiest for you to meet that design.
Here's some requirements off the top of my head:
Supports code beautifying of these languages: Ruby, Python, Perl
Output code behaves identically to input
Output has consistent use of tabs/spaces
Output has consistent function naming convention
Output has consistent variable naming convention
Output has matching braces and indentation
Make as many as you want, it's your program. ;p I was kidding about the Perl, but I think every language you support is going to add a more work.