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Why doesn't the example compile, aka how does (co-, contra-, and in-) variance work?
... so counter-intuitive, though it does have one very important application: functions.
trait Function1[-P, +R] {
def apply(p: P): R
}
Notice the "-" variance annotation on the P type parameter. This declaration as a whole means that Function1 is contravariant in P and covariant in R. Thus, we ...
What is the most efficient/elegant way to parse a flat table into a tree?
...g with this data to display a tree, I created a tree_item_iterator utility function which, for each node, should give you sufficient information to generate whatever kind of display you want.
More info about MPTT:
Trees in SQL
Storing Hierarchical Data in a Database
Managing Hierarchical Data in ...
Why should I not include cpp files and instead use a header?
...o when you include all the source files in your project together, there is fundamentally no difference between what you've done, and just making one huge source file without any separation at all.
"Oh, that's no big deal. If it runs, it's fine," I hear you cry. And in a sense, you'd be correct. ...
Best approach for designing F# libraries for use from both F# and C#
...
Daniel already explained how to define a C#-friendly version of the F# function that you wrote, so I'll add some higher-level comments. First of all, you should read the F# Component Design Guidelines (referenced already by gradbot). This is a document that explains how to design F# and .NET lib...
Build an ASCII chart of the most commonly used words in a given text [closed]
...76-length$w);$b="_"x($f/$q*$x);$_="|$b| $w ";$.>1or$_=" $b\n$_"'
for fun, here's a perl-only version (much faster):
~ % wc -c pgolf
204 pgolf
~ % cat pgolf
perl -lne'$1=~/^(the|and|o[fr]|to|.|i[tns])$/i||$f{lc$1}++while/\b([a-z]+)/gi}{@w=(sort{$f{$b}<=>$f{$a}}keys%f)[0..21];$Q=$f{$_=$w[...
How to Implement DOM Data Binding in JavaScript
...'d create a constructor that receives your element and some initial data.
function MyCtor(element, data) {
this.data = data;
this.element = element;
element.value = data;
element.addEventListener("change", this, false);
}
So here the constructor stores the element and data on prop...
How can I pair socks from a pile efficiently?
...
The best answer, IMO. While it's fun and clever (and appropriate for SO) to reduce a day-to-day problem to a computer algorithm, it makes much more sense to use the resolution power of man's eye/brain for a set as small as ~60 socks.
– ...
Is it ever advantageous to use 'goto' in a language that supports loops and functions? If so, why?
...s it ever advantageous to use goto in a language that supports loops and functions? If so, why?
25 Answers
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How to REALLY show logs of renamed files with git?
...s a small special case of "content" moving between paths. You might have a function that moves between files which a git user might trackdown with "pickaxe" functionalitly (e.g. log -S).
Other "path" changes include combining and splitting files; git doesn't really care which file you consider rena...
Abusing the algebra of algebraic data types - why does this work?
...jections fst : A×B → A and snd : A×B → B, where given any type C and functions f : C → A, g : C → B you can define the pairing f &&& g : C → A×B such that fst ∘ (f &&& g) = f and likewise for g. Parametricity guarantees the universal properties automatically an...