README.md
# lab42\_core
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Simple Ruby Core Module Extensions (for more see lab42\_more)
** Attention v0.6.0 pushes functional behavior to [lab42_function](https://github/RobertDober/lab42_function)**
## Programming Paradigms
### Functional
#### Fn/Fm - Functional Access To Methods
Can be used after `require 'lab42/core/fn'` **only**.
Might be moved into gem [lab42\_more](https://github.com/RobertDober/lab42_more) in the future .
API will remain the same, require will change to `require 'lab42_more/fn'`
##### fn like function
```ruby
Dir.files [APP_ROOT, 'spec', 'support', '**', '*.rb'], &Kernel.fn.require
Dir.files( %w{.. assets ** *.txt} ).sort_by &File.fn.mtime
```
##### fm like function/method
```ruby
%w{ alpha beta gamma delta }.sort_by &String.fm.size
```
**N.B.** This only works because the object behind the scenes of `Class#fm` knows how to bind
upon call, once it has been transformed by `#to_proc`
For details see the corresponding [Speculations](https://github.com/RobertDober/lab42_core/blob/master/speculations/fn.md).
#### Behave or B for Message Sending
This is a more general approach than `fn` or `fm` as we do not even know the class of the future receiver of the
message.
The subtle difference can be made clear with an example
```ruby
adder = B( :+ )
# can be used for Integers
adder.(1,41) # --> 42
# or Arrays
adder.(%w/a b/, %w&c d&) #--> %w%a b c d%
```
Which can of course not be accomplished by `Integer.fm.+`
For details see the corresponding [Speculations](https://github.com/RobertDober/lab42_core/blob/master/speculations/behave.md).
#### All Behavior is Composable
The above methods all return instances of `Behavior` and `Behavor` has a much richer API than Ruby's core _callables_ like `Proc` or `Method`
#### Memoization and Lazy Attributes
##### Memoization
is a, slightly forgotten, programming technique protecting against double calcultions.
This became extremly useful with [Dynamic Programming](https://en.wikipedia.org/wiki/Dynamic_programming#Dijkstra.27s_algorithm_for_the_shortest_path_problem) .
A much more simle example is allowing us to express and implement the [Fibonacci Sequence](https://en.wikipedia.org/wiki/Dynamic_programming#Fibonacci_sequence) in the same, some might say naïve, way.
Compared to the explicit memoization as shown in the Wikipedia article, which would read as follows in Ruby
```ruby
def fibo n, cache=[0, 1]
return cache[n] if cache[n]
cache[n] = fibo( n.pred, cache ) + fibo( n.pred.pred, cache )
end
```
It is still amazing how the specialized cache initialisation allows us to get rid of the original if statement.
However the general case would read like this
```ruby
def f n, cache = {}
args_hash = some_hash_fn n # n is all args here
return cache[args_hash] if cache[args_hash]
cache[args_hash] = f_implemenetation( some_fn(n), cache )
end
```
While a memoization mechanisme built into the language allos to write things like
```ruby
def_memoized f *args
...
end
def f *args
...
end
memoize :f
# Which can be written as
memoize \
def f *args
...
end
memoized do
def f *args
...
end
end
```
This gem opts for the `memoize` method in the `Module` class as this allows for
two different syntaxes
```ruby
memoize def f ...
end
#
def f ...
end
memoize :f
```
##### Lazy Attributes
Are just parameterless memoized methods, excatly the same as `let` bindings in [RSpec](http://www.rubydoc.info/gems/rspec-core/RSpec/Core/MemoizedHelpers/ClassMethods#let-instance_method).
```ruby
lazy_attr( :config ){ YAML.read config_file }
```
One could say they are just syntactic sugar for
```ruby
memoize def config
YAML.read config_file
end
```
One would be correct, but lazy attributes are many (in some of my modules and classes) and have a semantic role often very similar to
the example above. They are by nature static while methods like the shortest path or fibonacci are highly dynamic.
For details see the corresponding [Speculations](https://github.com/RobertDober/lab42_core/blob/master/speculations/memoization.md).
##### Gotchas
Do not, I repeat, **Do not** memoize methods with side effects!
The exception is _cached reading_ as in the example above.
Do not call memoized methods with arguments that cannot be used as Hash keys like e.g. BasicObject instances or other objects not responding to the **original** `hash` method.
## Core Extensions
### Array
Can be used after `require 'lab42/core'` or `require 'lab42/core/array'`
#### #flatten\_once
```ruby
[].flatten_once.assert.empty?
[[2, {a: 3}, [4]], {a: 5}].flatten_once.assert ==
[2, {a: 3}, [4], {a: 5}]
```
For details see the corresponding [Speculations](https://github.com/RobertDober/lab42_core/blob/master/speculations/array.md).
### Dir
Can be used after `require 'lab42/core'` or `require 'lab42/core/dir'`
```ruby
Dir.files "**/*" do | partial_path, full_path |
end
```
If only the relative or absolute pathes are needed there are the two variations avaiable:
```ruby
Dir.abs_files ...
Dir.rel_files ...
```
For details see the corresponding [Speculations](https://github.com/RobertDober/lab42_core/blob/master/speculations/dir.md).
### Enumerable
#### grep2
```ruby
enum.grep2 expr # ===>
enum.partition{ |ele| expr === ele }
```
#### to\_proc
And also `Enumerable#to\_proc` as e.g.
```ruby
counter = (1..3).to_proc
counter.().assert == 1
counter.().assert == 2
counter.().assert == 3
StopIteration.assert.raised? do
counter.()
end
```
For details see the corresponding [Speculations](https://github.com/RobertDober/lab42_core/blob/master/speculations/enumerable.md).
### File
#### #expand_local_path
`expand_local_path` to get rid of the `__FILE__` inside `expand_path`.
For details see the corresponding [Speculations](https://github.com/RobertDober/lab42_core/blob/master/speculations/file.md).
#### #if_readable
```ruby
File.if_readable 'some_file' do | file | # openes file as readable
end
```
#### #if_writeable
### Hash
#### #only
```ruby
{a: 42, b: 43}.only :a, :c # ===> {a: 42}
```
#### #fetch! (read fetch and set)
```ruby
a = {a: 42}
a.fetch!(b, 43) # or a.fetch!(b){43}
a == {a: 42, b: 43 } # true
```
**N.B.** Unlike `Hash#fetch` `Hash#fetch!` will **not** warn you that the block superseeds the default arg if both
are provided (after all there is a !).
For details see the corresponding [Speculations](https://github.com/RobertDober/lab42_core/blob/master/speculations/hash.md).
#### replace_rec
Recursive Replacement
##### Original Object untouched of course
```ruby
a = {a: 42, x: {a: 43}}
b = a.replace_rec( :a, &:succ )
a.assert == {a: 42, x: {a: 43}}
b.assert == {a: 43, x: {a: 44}}
```
For bulk replacements and how to specify limits, please refer to [Speculations](https://github.com/RobertDober/lab42_core/blob/master/speculations/hash.md).
#### without
```ruby
h = {a: 1, b: 2, c: 3}
h.without( :b, :c, :d ).assert == {a: 1}
h.assert == {a: 1, b: 2, c: 3}
```
### Object
Backport of `#itself` for versions < 2.2
### OpenObject
Immutable Open Objects
```ruby
x = OpenObject.new a: 42
x.a.assert == 42
x[:a].assert == 42
```
Immutability
All _modifications_ just return a new instance.
```ruby
x = OpenObject.new a: 42, b: 43
y = x.update a: 44
y.to_hash.assert == {a: 44, b: 43}
x.a.assert == 42
```
For details see the corresponding [Speculations](https://github.com/RobertDober/lab42_core/blob/master/speculations/open_object.md).
## Tools
### Console Tools
Can be used **only** after 'lab42/core/console_tools'.`
**N.B.** Never use in production code or applications. This code is extremly oriented console monkeypatching core classes massively.
This part is documented in [QED Console Tools](https://github.com/RobertDober/lab42_core/blob/master/speculations/console_tools.md).
## Author
Copyright © 2020,1 Robert Dober
robert.dober@gmail.com
## LICENSE
This software is licensed under Apache License v2.0. Please refer to [LICENSE](LICENSE) for details.
Versions strictly less to 0.5.2 of the Software can still be used under the MIT license.
<!-- SPDX-License-Identifier: Apache-2.0 -->