idioms – Page 3 – Tarik Billa

What is the idiomatic way to assoc several keys/values in a nested map in Clojure?

August 1, 2023 by Tarik

Here are a couple of ways. user> (update-in person [:name] assoc :first-name “Bob” :last-name “Doe”) {:name {:middle-name “Michael”, :last-name “Doe”, :first-name “Bob”}} user> (update-in person [:name] merge {:first-name “Bob” :last-name “Doe”}) {:name {:middle-name “Michael”, :last-name “Doe”, :first-name “Bob”}} user> (update-in person [:name] into {:first-name “Bob” :last-name “Doe”}) {:name {:middle-name “Michael”, :last-name “Doe”, :first-name “Bob”}} user> … Read more

Python “Every Other Element” Idiom [duplicate]

July 27, 2023 by Tarik

This will do it a bit more neatly: >>> data = [1,2,3,4,5,6] >>> zip(data[0::2], data[1::2]) [(1, 2), (3, 4), (5, 6)] (but it’s arguably less readable if you’re not familiar with the “stride” feature of ranges). Like your code, it discards the last value where you have an odd number of values.

Rails idiom to avoid duplicates in has_many :through

July 26, 2023 by Tarik

As long as the appended role is an ActiveRecord object, what you are doing: user.roles << role Should de-duplicate automatically for :has_many associations. For has_many :through, try: class User has_many :roles, :through => :user_roles do def <<(new_item) super( Array(new_item) – proxy_association.owner.roles ) end end end if super doesn’t work, you may need to set up … Read more

What is the idiomatic way to slice an array relative to both of its ends?

July 9, 2023 by Tarik

If you want to get n elements from the end of an array simply fetch the elements from -n to -1: PS C:\> $a = 0,1,2,3 PS C:\> $n = 2 PS C:\> $a[-$n..-1] 2 3 Edit: PowerShell doesn’t support indexing relative to both beginning and end of the array, because of the way $a[$i..$j] … Read more

Ruby idiom for substring from index until end of string

June 9, 2023 by Tarik

Ruby 2.6 introduced endless ranges, which basically remove the need to have to specify the end index. In your case, you can do: s = “hello world” s[6..]

Are one-line ‘if’/’for’-statements good Python style?

June 4, 2023 by Tarik

Well, if “exam” in “example”: print “yes!” Is this an improvement? No. You could even add more statements to the body of the if-clause by separating them with a semicolon. I recommend against that though.

Read a file and get an array of strings

May 28, 2023 by Tarik

DK.’s answer is quite right and has great explanation. However, you stated: Read a file and get an array of strings Rust arrays have a fixed length, known at compile time, so I assume you really mean “vector”. I would write it like this: use std::{ fs::File, io::{prelude::*, BufReader}, path::Path, }; fn lines_from_file(filename: impl AsRef<Path>) … Read more

What C++ idioms should C++ programmers use? [closed]

May 19, 2023 by Tarik

By far the single most important “pattern” to learn and know that’s (nearly) unique to C++ is RAII (Resource Acquisition Is Initialization). Edit: (To answer extra question edited into the question). You use RAII primarily to (semi-)automate resource management. The most obvious use is freeing resources owned by objects when the owning objects go out … Read more

C++ code for state machine

May 15, 2023 by Tarik

I was thinking in a more OO approach, using the State Pattern: The Machine: // machine.h #pragma once #include “MachineStates.h” class AbstractState; class Machine { friend class AbstractState; public: Machine(unsigned int _stock); void sell(unsigned int quantity); void refill(unsigned int quantity); unsigned int getStock(); ~Machine(); private: unsigned int stock; AbstractState *state; }; // ——– // machine.cpp … Read more

Idiomatic use of std::rel_ops

May 13, 2023 by Tarik

The way operator overloads for user defined classes was meant to work is via argument dependent lookup. ADL allows programs and libraries to avoid cluttering up the global namespace with operator overloads, but still allow convenient use of the operators; That is, without explicit namespace qualification, which is not possible to do with the infix … Read more