It gets its name from being the only operator in most languages taking three operands: a ? b : c The so-called "ternary operator", ?:, is closely related to the if- elseif- else syntax, but is used where a conditional choice between single expression values is required, as opposed to conditional execution of longer blocks of code. This error indicates that the conditional was of the wrong type: Int64 rather than the required Bool. Unlike C, MATLAB, Perl, Python, and Ruby – but like Java, and a few other stricter, typed languages – it is an error if the value of a conditional expression is anything but true or false: julia> if 1ĮRROR: TypeError: non-boolean (Int64) used in boolean context Note that very short conditional statements (one-liners) are frequently expressed using Short-Circuit Evaluation in Julia, as outlined in the next section. This value is simply the return value of the last executed statement in the branch that was chosen, so julia> x = 3 If blocks also return a value, which may seem unintuitive to users coming from many other languages. The following change to the above function results in a runtime error julia> function test(x,y)ĮRROR: UndefVarError: `relation` not defined However, when depending on this behavior, make sure all possible code paths define a value for the variable. The variable relation is declared inside the if block, but used outside. So, we could have defined the test function above as julia> function test(x,y) This means that new variables defined inside the if clauses can be used after the if block, even if they weren't defined before. The condition expressions in the if- elseif- else construct are evaluated until the first one evaluates to true, after which the associated block is evaluated, and no further condition expressions or blocks are evaluated. The elseif and else blocks are optional, and as many elseif blocks as desired can be used. Here it is in action: julia> function test(x, y) If the condition expression x y is evaluated, and if it is true, the corresponding block is evaluated if neither expression is true, the else block is evaluated. Here is the anatomy of the if- elseif- else conditional syntax: if x y Although it is typical, there is no requirement that begin blocks be multiline or that chains be single-line: julia> begin x = 1 y = 2 x + y endĬonditional evaluation allows portions of code to be evaluated or not evaluated depending on the value of a boolean expression. This syntax is particularly useful with the terse single-line function definition form introduced in Functions. Since these are fairly small, simple expressions, they could easily be placed onto a single line, which is where the chain syntax comes in handy: julia> z = (x = 1 y = 2 x + y) Here's an example of a begin block: julia> z = begin The value of both compound expression constructs is that of the last subexpression. There are two Julia constructs that accomplish this: begin blocks and chains. Sometimes it is convenient to have a single expression which evaluates several subexpressions in order, returning the value of the last subexpression as its value. Everyday programming requires no direct usage of tasks, but certain problems can be solved much more easily by using tasks. This is a powerful construct: both exception handling and cooperative multitasking are implemented in Julia using tasks. Tasks are not so standard: they provide non-local control flow, making it possible to switch between temporarily-suspended computations. The first five control flow mechanisms are standard to high-level programming languages. Exception Handling: try- catch, error and throw.Repeated Evaluation: Loops: while and for.Short-Circuit Evaluation: logical operators & (“and”) and || (“or”), and also chained comparisons.Conditional Evaluation: if- elseif- else and ?: (ternary operator).Julia provides a variety of control flow constructs: Instrumenting Julia with DTrace, and bpftrace.Reporting and analyzing crashes (segfaults). Static analyzer annotations for GC correctness in C code.Proper maintenance and care of multi-threading locks.printf() and stdio in the Julia runtime.Talking to the compiler (the :meta mechanism).High-level Overview of the Native-Code Generation Process.Noteworthy Differences from other Languages.Multi-processing and Distributed Computing.Mathematical Operations and Elementary Functions.
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