colon-equals
What does the := operator mean in mysql?
In MySQL, := is an assignment operator: SELECT @foo := ‘bar’; // variable ‘foo’ now has value ‘bar’ return value: ‘bar’ while = is an equality test: SELECT @foo = ‘hi mom’; // does variable ‘foo’ have the value ‘hi mom’; return value: false (‘bar’ == ‘hi mom’ -> false) Note that you CAN do … Read more
Bash script what is := for?
From Bash Reference Manual: ${parameter:=word} If parameter is unset or null, the expansion of word is assigned to parameter. The value of parameter is then substituted. Positional parameters and special parameters may not be assigned to in this way. Basically it will assign the value of word to parameter if and only if parameter is … Read more
var vs := in Go
In Go, top-level variable assignments must be prefixed with the var keyword. Omitting the var keyword is only allowed within blocks. package main var toplevel = “Hello world” // var keyword is required func F() { withinBlock := “Hello world” // var keyword is not required }
The forgotten assignment operator “=” and the commonplace “:=”
In PL/PgSQL parser, assignment operator is defined as assign_operator : ‘=’ | COLON_EQUALS ; This is a legacy feature, present in source code since 1998, when it was introduced – as we can see in the PostgreSQL Git repo. Starting from version 9.4 it is oficially documented. This idiosyncrasy – of having two operators for … Read more
What is the difference between = and := in Scala?
= in scala is the actual assignment operator — it does a handful of specific things that for the most part you don’t have control over, such as Giving a val or var a value when it’s created Changing the value of a var Changing the value of a field on a class Making a … Read more
What is the difference between := and = in Go?
= is assignment. more about assignment in Go: Assignments The subtle difference between = and := is when = used in variable declarations. General form of variable declaration in Go is: var name type = expression the above declaration creates a variable of a particular type, attaches a name to it, and sets its initial … Read more
:= vs = in make macros [duplicate]
Variables defined with := in GNU make are expanded when they are defined rather than when they are used.
When should I use the := operator in data.table?
Here is an example showing 10 minutes reduced to 1 second (from NEWS on homepage). It’s like subassigning to a data.frame but doesn’t copy the entire table each time. m = matrix(1,nrow=100000,ncol=100) DF = as.data.frame(m) DT = as.data.table(m) system.time(for (i in 1:1000) DF[i,1] <- i) user system elapsed 287.062 302.627 591.984 system.time(for (i in 1:1000) … Read more