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109 lines
2.1 KiB
Markdown
109 lines
2.1 KiB
Markdown
# Tips
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## Want to change the language in which errors are displayed
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Please download Erg for your language.
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However, external libraries may not support multiple languages.
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## Want to change only certain attributes of a record
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```python
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record: {.name = Str; .age = Nat; .height = CentiMeter}
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{height; *rest} = record
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mut_record = {.height = !height; *rest}
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```
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## Want to shadow variables
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Shadowing in the same scope is not possible with Erg. However, you can redefine them if the scope changes (This is a syntax called instance block).
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````python
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## Get a T!-type object and finally assign it to a variable as type T
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x: T =
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x: T! = foo()
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x.bar!()
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x.freeze()
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````
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## Want to reuse a final class (non-inheritable class) somehow
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You can create a wrapper class. This is a so-called composition pattern.
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```python
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FinalWrapper = Class {inner = FinalClass}
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FinalWrapper.
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method self =
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self::inner.method()
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...
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```
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## Want to enumerate at the beginning of 1
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method 1:
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```python
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arr = [...]
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for! arr.iter().enumerate(start := 1), i =>
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...
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```
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method 2:
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```python
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arr = [...]
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for! arr.iter().zip(1..) , i =>
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...
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```
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## Want to test a (white box) non-public API
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The private API in `foo.er` is specially accessible in the module `foo.test.er`.
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The `foo.test.er` module cannot be imported, so it remains hidden.
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```python
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# foo.er
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private x = ...
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```
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```python
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# foo.test.er
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foo = import "foo"
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@Test
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'testing private' x =
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...
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y = foo::private x
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...
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```
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## Want to define a (variable) attribute that is read-only from the outside
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You can make the attribute private and define a getter.
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```python
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C = Class {v = Int!}
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C::
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inc_v!(ref! self) = self::v.inc!()
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...
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C.
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get_v(ref self): Int = self::v.freeze()
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...
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```
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## When implementing a trait's methods, warnings are given for variables that were not used
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You can use `discard` or `_ = ...`.
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```python
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T = Trait {.f = (Self, x: Int, s: Str) -> Int}
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C = Class T
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C|<: T|.
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f self, x, s =
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discard s # or _ = s
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...
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```
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## Want to stop warnings
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There is no option in Erg to stop warnings (this is by design). Please rewrite your code.
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