Declare type of struct field to be the same type as the struct itself in Julia

See also questions close to this topic

• How is exception handling implemented in Python?

  This question asked for explanations of how exception handling is implemented under the hood in various languages but it did not receive any responses for Python.

  I'm especially interested in Python because Python somehow "encourages" exception throwing and catching via the EAFP principle.

  I've learned from other SO answers that a try/catch block is cheaper than an if/else statement if the exception is expected to be raised rarely, and that it's the call depth that's important because filling the stacktrace is expensive. This is probably principally true for all programming languages.

  Are there any resources that explain how the Python exception handling was implemented internally and if special optimizations were made because of the EAFP principle?
• Error-26499:InternalError-Invalid mptNetHandledTask=06C4BD90/ mptNetVUserVars=06CA2CEO/ptTaskItem=069659D0/ptVUserVars=05F0C040/ptSocket=00000000/meMa

  Error-26499:InternalError-Invalid mptNetHandledTask=06C4BD90/ mptNetVUserVars=06CA2CEO/ptTaskItem=069659D0/ptVUserVars=05F0C040/ptSocket=00000000/meMaxTaskState=36=dummy_last_statein feProcessorSocket inLrwNetSocket.cpp
• Most efficient way of finding dictionary values by (a larg list) of keys? Python 3.8

  I have the following dictionary:

  d = {"sadsa": 4, "awdwa" 13, ,"tdadq": 2 ...} composed of 100000 items

  Now i have a list of around 1000 items: l = ["awdwa", "fdafs", ...]

  What is the fastest way to retrieve all matching values?

  Currently Im trying the following method:

  • [d[i] for i in l if i in d]

  Is there a faster way?

  I read something about ordering, but im not sure what it means. Is it related to binary search?

  How does the dictionary get value by key, works ... does it iterate through all keys until finding the matching one?
• Cart is being reset back to zero once my function ends

  Help Cart is being reset back to zero once my function ends.

  My item is being created, and the fields populated. once my add item function runs it adds the item to the cart.cartItems array and increments the size. once the function ends the array is rest back to zero instead of having my recently added item. enter image description here

  ShoppingCart AddItem(ItemToPurchase item, ShoppingCart cart){

  if( cart.cartSize < MAX_CART_SIZE ){
     
      cart.cartItems[cart.cartSize] = item; 
     cart.cartSize++;
      } 
  
  else{
      printf("Cart it full, item can not be added\n");
  }
  
  return cart; 
  
• Create an array of structs swift

  struct Section {
  var date: Date
  var transactions: [Transaction] // array of my custom realm objects
  }
  
  @objcMembers class Transaction: Object {
  dynamic var id:               String = UUID().uuidString
  dynamic var time:             Int64 = 0
  dynamic var details:          String = "" // description
  dynamic var mcc:              Int32 = 0
  dynamic var hold:             Bool = false
  dynamic var amount:           Int64 = 0
  dynamic var operationAmount:  Int64 = 0
  dynamic var currencyCode:     Int32 = 0
  dynamic var commissionRate:   Int64 = 0
  dynamic var cashbackAmount:   Int64 = 0
  dynamic var balance:          Int64 = 0
  dynamic var comment:          String = ""
  dynamic var emoji:            String = "❓"
  
  var sectionDict: [Section] = []
  
  func convert(_ transactions: Results<Transaction>) -> [Section] {
      let section = Section(date: Date(), transactions: [Transaction()])
      sectionDict.append(section)
      return sectionDict
   }
  
  
  let section = Section(date: Date(), transactions: [Transaction])
  

  I get an error when trying to create an array of structs: Cannot convert value of type '[Transaction].Type' to expected argument type '[Transaction]'

  Can't figure out what's the problem. As result i'm trying to store all my Transactions objects into let section arr.
• Expression "passing by reference" for structs in C

  I have recently had a class about structures in C and the lecturer used the expression "pass by reference" to describe the action of passing a pointer towards a structure to a function. I have always read that C does not have "pass by reference" because, unlike Cpp, pass by reference can only be emulated by passing by value a pointer towards some object — and we should rather say "pass by pointer". So I am wondering whether or not things work differently for structures and this expression is justified in this context.
• Find the name of the Imported DLLs using PE Headers

  A Few days back I have started with Windows System Programming using c++. Hence, thought of building a utility to grab the PE Headers of an exe file. And now I am stuck with the Image_Import_descriptor structure.

  What I want is to get the names of the DLL files(modules) imported by the exe. And below is the code I am using to get those names:

          DWORD Image_Import_Descriptor_addr = (DWORD)ntHeader + (DWORD)sizeof(ntHeader->FileHeader) + (DWORD)ntHeader->FileHeader.SizeOfOptionalHeader + (DWORD)ntHeader->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_IMPORT].Size;
          importImageDescriptor = (PIMAGE_IMPORT_DESCRIPTOR)Image_Import_Descriptor_addr;
  

  To get the RVA of the name:

          DWORD name = importImageDescriptor->Name;
          printf("\n\n\n\t\t (((Module Name)): %X", name);
  

  Gives an output: 4778B00

  Hope untill now everything was fine technically.

  However, my motive is to print the DLL names(like kernel32.dll). Can anyone help me out how to get the names of the DLL ?

  My workarounds:

              LPCSTR snames = (LPCSTR)name;          
              printf("\n\n\n\t\t (((Module Name)): %s", *snames);
  

  But this is giving me an error: Access Violation

  I am getting confused with the pointers and Datatype conversions. A help is much appreciated.
• When should TypeApplications be preferred over simple :: signatures or ScopedTypeVariables?

  Considering this simple example of ambiguous type inference:

  #! /usr/bin/env stack
  {- stack runghc -}
  
  {-# LANGUAGE ScopedTypeVariables #-}
  {-# LANGUAGE TypeApplications #-}
  
  main :: IO ()
  main = do
    -- This will fail to compile without additional type info
    -- let w = read "22"
    -- print w
    
    -- My go-to for this is type signatures in the expressions
    let x = read "33" :: Integer
    print x 
    
    -- Another possibility is ScopedtypeVariables
    let y :: Integer = read "44"
    print y
    
    -- How does TypeApplications differ from the code above? When should this be chosen instead?
    let z = read @Integer "55"
    print z
  

  My question is, in cases like this, is there an advantage to using TypeApplications?
• Swift type erasure with property wrapper

  Im struggling a little bit with the implementation of type-erasure in Swift.

  I have a property wrapper ThemeValue which is a generic wrapper around Tweakable, in this case String or CGFloat both conform to Tweakable

  What I am trying to achieve is to be able to get all the ThemeValues associated to the struct

  I feel like I am fundamentally misunderstanding something here.

  protocol Themeable {
    var tweakables: [ThemeValue<AnyTweakable>] { get }
  }
  
  extension Themeable {
    var tweakables: [ThemeValue<AnyTweakable>]
      // What I want to do is return all ThemeValues instance variables to this struct 
      let themeValues = Mirror(respresenting: self).children.compactMap {
         // return $0.value as? ThemeValue<AnyTweakable>
      }
    }
  }
  
  struct ExampleThemeable: Themeable {
      let identifier: String = UUID().uuidString
      @ThemeValue<String>(key: "stringExample", defaultValue: "foo") public var stringExample
      @ThemeValue<CGFloat>(key: "floatExample", defaultValue: 0) public var floatExample
  }
  

  enum TweakableType {
      case any
      case string
      case cgFloat
  }
  
  protocol Tweakable {
      var type: TweakableType { get }
      var stringValue: String { get }
  }
  
  extension String: Tweakable {
      var type: TweakableType { return .string }
      var stringValue: String { return self }
  }
  
  extension CGFloat: Tweakable {
      var type: TweakableType { return .cgFloat }
      var stringValue: String { return "\(self)" }
  }
  
  struct AnyTweakable: Tweakable {
      var type: TweakableType { return .any }
      var stringValue: String = ""
  }
  
  @propertyWrapper
  struct ThemeValue<T: Tweakable> {
  
      private let key: String
      let defaultValue: T
      var currentValue: T
  
      init(key: String, defaultValue: T) {
          self.key = key
          self.defaultValue = defaultValue
          self.currentValue = defaultValue
      }
  
      var wrappedValue: T {
          get {
              return currentValue
          }
          set {
              self.currentValue = newValue
          }
      }
  }
  
• Julia: Writing a function "paramvalues" that returns a dictionary of parameter values

  I am working on an Economics assignment and need to create a function in Julia that takes keyword arguments and returns them in the form of a dictionary. So far this is my code, but it is not running because there is "no method matching getindex(::Nothing, ::Symbol).

  function paramvalues(a; Nb = 100, Ns = 100, Minval = 0, Maxval = 200, Mincost = 0, Maxcost = 200)
      d = Dict(:Nb => Nb, :Ns => Ns, :Minval => Minval, :Maxval => Maxval, :Mincost => Mincost, :Maxcost => Maxcost)
      for values in a
          d[values] = get(d, values, 0) 
      end
      d 
  end
  
• Top level scope and bound errors in Julia

  Hi all I have the following function. This is a function I made in Python that basically gives me an array of arrays, depending on which integer I feed to the function. The integer is basically the number of hexagons I include in my function.

  function hex_index(N)
      
      x,y,z=0,0,0
      count,mth_cell = 0,0
      index_of_cells = [0,0,0]
      sixth = 1
  
      while count <= N
          sixth = 1
          mth_cell = 0
  
          for i= 1:6*count
  
              if mth_cell==count
                  mth_cell=0
                  sixth += 1 
  
              elseif sixth==2
                   x=0
                   y=count-mth_cell
                   z=-count+mth_cell
  
              elseif sixth==3
                   x=-mth_cell
                   y=0
                   z=-count+mth_cell
  
              elseif sixth==4
                   x=-count+mth_cell
                   y=-mth_cell
                   z=0
              
              elseif sixth==5
                   x=0
                   y=-count+mth_cell
                   z=mth_cell
  
              elseif sixth==6
                   x=mth_cell
                   y=0
                   z=count-mth_cell  
              end
              
              curr_cell_index=[x,y,z]
              append!(index_of_cells, curr_cell_index)
              mth_cell=+1
    
          end
  
          count+=1
      end
  
      index_G2_G1=[]
      element=[]
  
      for i in index_of_cells
          g3=i[1]
          g3=i[2]
          g3=i[3]
  
          element=[g2+g3,g1+g3]
  
          append!(index_G2_G1,element)
      end
  
      return(index_G2_G1)
  end
  
  index = hex_index(N)
  
  
  

  And it returns the following error:

  BoundsError
  
  Stacktrace:
   [1] getindex at .\number.jl:78 [inlined]
   [2] hex_index(::Int64) at .\In[18]:58
   [3] top-level scope at In[18]:69
   [4] include_string(::Function, ::Module, ::String, ::String) at .\loading.jl:1091
  
  

  I am not sure why? I am new to Julia and do not really understand the scope issue in Julia. I come from using Python...
• Kriging interpolation using GeoStats package in Julia

  I am trying to build a model for kriging interpolation using GeoStats package in julia. I have tried an example of 2D interpolations but the results are not accurate, as mentioned below.

  Code for 2D interpolation:

  
  using KrigingEstimators, DataFrames, Variography, Plots
  
  OK = OrdinaryKriging(GaussianVariogram()) # interpolator object
  
  f(x) = sin(x)
  
  # fit it to the data:
  x_train = range(0, 10.0, length = 9) |> collect
  y_train = f.(x_train)
  scatter(x_train, y_train, label="train points")
  
  x_train = reshape(x_train, 1, length(x_train))
  
  krig = KrigingEstimators.fit(OK, x_train, y_train) # fit function
  
  result = []
  variance =[]
  test = range(0, 10, length = 101) |> collect
  y_test = f.(test)
  test = reshape(test, 1, length(test))
  for i in test
      μ, σ² = KrigingEstimators.predict(krig, [i])
      push!(result, μ)
      push!(variance, σ²)
  end
  df_krig_vario = DataFrame(:predict=>result, :real=>y_test, :variance=>variance)
  println(first(df_krig_vario, 5))
  mean_var = sum(variance)/length(variance)
  println("")
  println("mean variance is $mean_var")
  test = reshape(test, length(test), 1)
  plot!(test, y_test, label="actual")
  plot!(test, result, label="predict", legend=:bottomright, title="Gaussian Variogram")
  

  

  With reference to the above figure it can be seen that the interpolation prediction is not accurate. May I know, how to improve this accuracy?
• How to create space-holder when field is empty or null?

  The "locus" field displays a series of values.

  I would like the values to display in a specific order AND I would like the empty or null fields to create a space-holder so that each value repeats in the same space in the following sections.

  In the attached pictures, the values are grouped by sample date (also the details section is formatted with multiple columns).

  Thank you!

  design preview
• How to define React component with conditional props interface?

  i need to define "Field" component that renders textarea or input depends on prop multiline

  I trying to do this like that:

  import React from 'react';
  
  type Props<T extends boolean = boolean> = { multiline: T } & T extends true 
      ? React.HTMLProps<HTMLTextAreaElement> 
      : React.HTMLProps<HTMLInputElement>
  
  export const Field: React.FC<Props> = ({ multiline, ...props }) => { // error here
      const Element = multiline ? 'textarea' : 'input';
  
      return <Element {...props} onInput={e => {}} />; // error here
  }
  
  // usage
  
  const result = (
      <Field onChange={e => console.log(e.target.value)} /> // error here
  );
  

  But typescript provide several errors like:

  1 Property 'multiline' does not exist on type 'HTMLProps<HTMLInputElement> & { children?: ReactNode; }'.(2339)
  
  2 [large error, more in playground]
  
  3 Property 'value' does not exist on type 'EventTarget'.(2339)
  
  

  Playground here

  How can i define such component?
• Drupal hook to add label in multi-value field

  I want to create Multi-value Drupal field programmatically.

  I want to create a field with five input fields, of text-type full-html and I want to show labels to the left of the fields.

  Type of field : This will be full HTML

  What is the correct hook to create fields programmatically, and add labels to the fields left. The fields input will be shown only in edit page field.

  

  I want to add labels to the label, how to proceed to add labels to the input field programmatically.