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The Interactive Data Language (IDL) is a high-level programming language primarily used for data analysis and visualization. First developed in the 1970s by David Stern at Research Systems, Inc., IDL has become a standard tool for astronomers and atmospheric scientists (Stern, D., 2001). The language's array-oriented operations and powerful graphics capabilities make it ideal for processing large volumes of data. It is also popular in medical imaging and remote sensing fields due to its ability to handle multi-dimensional arrays efficiently. Despite competition from open-source languages like Python, IDL's robustness continues to make it a reliable choice in scientific computing (Bowman, C., 2014).

Ask the right questions secure the right IDL talent among an increasingly shrinking pool of talent.

First 20 minutes

General IDL app knowledge and experience

The first 20 minutes of the interview should seek to understand the candidate's general background in IDL application development, including their experience with various programming languages, databases, and their approach to designing scalable and maintainable systems.

How would you describe the basic structure of an IDL file?

An IDL file typically contains a module that includes interfaces, methods, and data types. The interface defines methods and their parameters. Data types can be native or custom defined.

What are the key data types in IDL?

IDL supports several data types including integer, float, double, string, boolean, byte, object references, arrays, and enumerations.

How would you handle errors in IDL?

IDL provides a system variable !ERROR_STATE which can be used to handle errors. It contains several fields like NAME, BLOCK, CODE, etc., which can be used to get information about the error.

What are the uses of IDL arrays?

IDL arrays are used to store multiple values of the same data type. They are useful in performing vectorized operations, which can greatly improve the performance of the code.

Describe the difference between an IDL procedure and an IDL function.

An IDL procedure performs a task and does not return a value, whereas an IDL function performs a task and returns a value.

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What you’re looking for early on

Does the candidate have a strong understanding of IDL programming language?

Has the candidate demonstrated problem-solving skills?

Is the candidate able to communicate effectively?

Does the candidate have experience with other programming languages?

Next 20 minutes

Specific IDL development questions

The next 20 minutes of the interview should focus on the candidate's expertise with specific backend frameworks, their understanding of RESTful APIs, and their experience in handling data storage and retrieval efficiently.

How would you create a multidimensional array in IDL?

A multidimensional array can be created in IDL using the ARRAY function. For example, ARRAY(3,3,3) creates a 3x3x3 dimensional array.

What are the key elements of an IDL interface?

An IDL interface typically contains methods and attributes. Methods define the operations that can be performed, and attributes define the data that can be accessed.

How would you handle memory management in IDL?

IDL provides several functions for memory management like PTR_FREE, HEAP_GC, etc. It's important to free up memory that is no longer needed to prevent memory leaks.

Describe the difference between arrays and lists in IDL.

Arrays in IDL are of fixed size and all elements must be of the same type. Lists, on the other hand, can grow dynamically and can contain elements of different types.

How would you implement object-oriented programming in IDL?

IDL provides a class definition syntax for defining classes and objects. It supports key OOP concepts like inheritance, encapsulation, and polymorphism.

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At this point, a skilled IDL engineer should demonstrate strong problem-solving abilities, proficiency in IDL programming language, and knowledge of software development methodologies. Red flags include lack of hands-on experience, inability to articulate complex concepts, or unfamiliarity with standard coding practices.

Digging deeper

Code questions

These will help you see the candidate's real-world development capabilities with IDL.

What does this simple IDL code snippet do?
print, 'Hello, World!'
This is a simple 'Hello, World!' program in IDL. It prints the string 'Hello, World!' to the console.
What does this IDL syntax represent?
a = findgen(10)
This code generates a one-dimensional floating-point array of 10 elements. The array elements start from 0 and increment by 1 for each subsequent element.
What will be the output of this IDL array manipulation code?
a = indgen(10) 
 b = a[5:8]
This code first creates an integer array 'a' with elements from 0 to 9. Then it creates a subarray 'b' from 'a' with the elements from index 5 to 8. So, 'b' will be [5, 6, 7, 8].
What does this IDL code do, which involves threading concepts?
thread, /JOIN_ALL
This code waits for all threads to finish executing. It's a way to ensure that all threads have completed their tasks before the program proceeds.

Wrap-up questions

Final candidate for IDL Developer role questions

The final few questions should evaluate the candidate's teamwork, communication, and problem-solving skills. Additionally, assess their knowledge of microservices architecture, serverless computing, and how they handle IDL application deployments. Inquire about their experience in handling system failures and their approach to debugging and troubleshooting.

What are the advantages of using IDL's object graphics over direct graphics?

Object graphics in IDL provide a higher level of abstraction and flexibility compared to direct graphics. They allow for interactive manipulation of graphics and better control over the layout.

Describe the difference between local and global variables in IDL.

Local variables are defined within a function or procedure and can only be accessed within that scope. Global variables are defined outside all functions and procedures and can be accessed anywhere in the program.

How would you optimize performance in IDL?

Performance in IDL can be optimized by using vectorized operations, managing memory efficiently, and using compiled routines instead of interpreted ones.

IDL application related

Product Perfect's IDL development capabilities

Beyond hiring for your IDL engineering team, you may be in the market for additional help. Product Perfect provides seasoned expertise in IDL projects, and can engage in multiple capacities.

IDL Consultive assessments

IDL Application Conversion Assessment IDL Application Integration Assessment IDL Data & Database Integration Assessment

Custom IDL development projects

Custom IDL App Conversion IDL Custom App Development Process App UI Design for IDL Facelifts

Hiring guide for IDL Engineers

IDL Developer Hiring Guide

What you’re looking for early on

The ideal back-end app developer

What you’re looking to see on the IDL engineer at this point.

IDL Consultive assessments

Custom IDL development projects