Elixir Book Pdf
Cris Luczak
You misread his reply but keep in mind this is not a good way to approach the discussion. We will definitely make mistakes as we implement the type system and I hope the feedback will be more constructive than the above.
If I get this correctly, being the nature of gradual typing systems, I assume these signatures will not be mandatory in every function. If this is the case, then I believe this greatly benefits elixir:
And while I am admittedly biased towards having a strong typing system, I still want to publicly state that I (and my team) have great expectations in regards to this system and eagerly await your next move/news on it.
Kernel provides the basic capabilities the Elixir standard libraryis built on top of. It is recommended to explore the standard libraryfor advanced functionality. Here are the main groups of modules in thestandard library (this list is not a complete reference, see thedocumentation sidebar for all entries).
Protocols add polymorphic dispatch to Elixir. They are contractsimplementable by data types. See Protocol for more information onprotocols. Elixir provides the following protocols in the standard library:
This module includes the built-in guards used by Elixir developers.They are a predefined set of functions and macros that augment patternmatching, typically invoked after the when operator. For example:
The clause above will only be invoked if the user's age is more thanor equal to 16. Guards also support joining multiple conditions withand and or. The whole guard is true if all guard expressions willevaluate to true. A more complete introduction to guards is availablein the Patterns and guards page.
This is possible so Elixir developers can create collections, such asdictionaries and ordered sets, that store a mixture of data types in them.To understand why this matters, let's discuss the two types of comparisonswe find in software: structural and semantic.
Structural means we are comparing the underlying data structures and we oftenwant those operations to be as fast as possible, because it is used to powerseveral algorithms and data structures in the language. A semantic comparisonworries about what each data type represents. For example, semanticallyspeaking, it doesn't make sense to compare Time with Date.
One example that shows the differences between structural and semanticcomparisons are strings: "alien" sorts less than "office" ("alien" < "office")but "lien" is greater than "office". This happens because
This means comparisons in Elixir are structural, as it has the goalof comparing data types as efficiently as possible to create flexibleand performant data structures. This distinction is specially importantfor functions that provide ordering, such as >/2, =/2,
will return true because structural comparison compares the :dayfield before :month or :year. Luckily, the Elixir compiler willdetect whenever comparing structs or whenever comparing code that iseither always true or false, and emit a warning accordingly.
The second argument is precisely the module to be used for semanticcomparison. Keeping this distinction is important, because if semanticcomparison was used by default for implementing data structures andalgorithms, they could become orders of magnitude slower!
Finally, note there is an overall structural sorting order, called"Term Ordering", defined below. This order is provided for referencepurposes, it is not required by Elixir developers to know it by heart.
When comparing two numbers of different types (a number being eitheran integer or a float), a conversion to the type with greater precisionwill always occur, unless the comparison operator used is either ===/2or !==. A float will be considered more precise than an integer, unlessthe float is greater/less than +/-9007199254740992.0 respectively,at which point all the significant figures of the float are to the leftof the decimal point. This behavior exists so that the comparison of largenumbers remains transitive.
Some of the functions described in this module are inlined bythe Elixir compiler into their Erlang counterparts in the:erlang module.Those functions are called BIFs (built-in internal functions)in Erlang-land and they exhibit interesting properties, as someof them are allowed in guards and others are used for compileroptimizations.
The complexity of a ++ b is proportional to length(a), so avoid repeatedlyappending to lists of arbitrary length, for example, list ++ [element].Instead, consider prepending via [element rest] and then reversing.
If the right operand is not a proper list, it returns an improper list.If the left operand is not a proper list, it raises ArgumentError.If the left operand is an empty list, it returns the right operand.
Unlike Erlang, such attributes are not stored in the module by default sinceit is common in Elixir to use custom attributes to store temporary data thatwill be available at compile-time. Custom attributes may be configured tobehave closer to Erlang by using Module.register_attribute/3.
It is important to note that reading an attribute takes a snapshot ofits current value. In other words, the value is read at compilationtime and not at runtime. Check the Module module for other functionsto manipulate module attributes.
As mentioned above, every time you read a module attribute, a snapshotof its current value is taken. Therefore, if you are storing largevalues inside module attributes (for example, embedding external filesin module attributes), you should avoid referencing the same attributemultiple times. For example, don't do this:
This is similar to binary_part/3 except that if start + sizeis greater than the binary size, it automatically clips it tothe binary size instead of raising. Opposite to binary_part/3,this function is not allowed in guards.
One of the benefits of dbg/2 is that its debugging logic is configurable,allowing tools to extend dbg with enhanced behaviour. This is done, forexample, by IEx which extends dbg with an interactive shell where youcan directly inspect and access values.
The debug function can be configured at compile time through the :dbg_callbackkey of the :elixir application. The debug function must be amodule, function, args tuple. The function function in module will beinvoked with three arguments prepended to args:
By default, the debug function we use is Macro.dbg/3. It just printsinformation about the code to standard output and returns the valuereturned by evaluating code. options are used to control how termsare inspected. They are the same options accepted by inspect/2.
The compiler translates this into multiple functions with different arities,here MyMath.multiply_by/1 and MyMath.multiply_by/2, that represent cases whenarguments for parameters with default values are passed or not passed.
Function and variable names in Elixir must start with an underscore or aUnicode letter that is not in uppercase or titlecase. They may continueusing a sequence of Unicode letters, numbers, and underscores. They mayend in ? or !. Elixir's Naming Conventionssuggest for function and variable names to be written in the snake_caseformat.
Functions defined with defdelegate/2 are public and can be invoked fromoutside the module they're defined in, as if they were defined using def/2.Therefore, defdelegate/2 is about extending the current module's public API.If what you want is to invoke a function defined in another module withoutusing its full module name, then use alias/2 to shorten the module name or useimport/2 to be able to invoke the function without the module name altogether.
exception/1 - receives the arguments given to raise/2and returns the exception struct. The default implementationaccepts either a set of keyword arguments that is merged intothe struct or a string to be used as the exception's message.
message/1 - receives the exception struct and must return itsmessage. Most commonly exceptions have a message field whichby default is accessed by this function. However, if an exceptiondoes not have a message field, this function must be explicitlyimplemented.
Note the convention in Elixir is to prefix all guards that return a booleanwith the is_ prefix, such as is_list/1. If, however, the function/macroreturns a boolean and is not allowed in guards, it should have no prefix andend with a question mark, such as Keyword.keyword?/1.
Module names (and aliases) must start with an ASCII uppercase character whichmay be followed by any ASCII letter, number, or underscore. Elixir'sNaming Conventions suggest for module names and aliasesto be written in the CamelCase format.
In the example above, two modules - Foo and Foo.Bar - are created.When nesting, Elixir automatically creates an alias to the inner module,allowing the second module Foo.Bar to be accessed as Bar in the samelexical scope where it's defined (the Foo module). This only happensif the nested module is defined via an alias.
If the Foo.Bar module is moved somewhere else, the references to Bar inthe Foo module need to be updated to the fully-qualified name (Foo.Bar) oran alias has to be explicitly set in the Foo module with the help ofalias/2.
Elixir will accept any module name as long as the expression passed as thefirst argument to defmodule/2 evaluates to an atom.Note that, when a dynamic name is used, Elixir won't nest the name underthe current module nor automatically set up an alias.
Use defoverridable with care. If you need to define multiple moduleswith the same behaviour, it may be best to move the default implementationto the caller, and check if a callback exists via Code.ensure_loaded?/1 andfunction_exported?/3.
Private functions are only accessible from within the module in which they aredefined. Trying to access a private function from outside the module it'sdefined in results in an UndefinedFunctionError exception.
A struct is a tagged map that allows developers to providedefault values for keys, tags to be used in polymorphicdispatches and compile time assertions. For more informationabout structs, please check %/2.
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