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Developers who can code in Apple's Swift programming language have been the most in demand over the past year, according to new figures from Toptal.

The freelance developer placement firm looked at year-on-year growth in job requests for each language and found that requests for Swift projects rose 600 percent in 2015, roughly triple the rate of many other languages.

Requests for HTML jobs grew 267 percent, followed by 244 percent growth for C++ requests, and 239 percent growth for CSS.

PHP, Sass, Objective-C, Less, XML, and Python recorded growth in a range between 167 percent and 120 percent, according to Toptal, which said its data was based on tens of thousands of companies looking for talent.

Apple only released Swift in June 2014, so high growth could be expected, given a lower starting point than more established languages and the popularity of Apple's iOS devices. Still, other studies based on GitHub references have also found Swift displaying unprecedented growth among developers.

Swift's ascent should be supported further by Apple's move in December to open-source the language. Apple's enterprise partner IBM almost immediately leapt on it to create the IBM Swift sandbox, which allows developers to test Swift code in the cloud.

However, Java is still the most popular language for building mobile apps, according to a recent study by mobile ad network InMobi. In a survey of 1,085 mobile app developers, it found that 65 percent of developers preferred Java.

HTML5 was the second most popular with 45 percent of mobile developers using it, followed by JavaScript and Objective C, preferred respectively by 44 percent and 36 percent of respondents.

Meanwhile, 18 percent of app developers reported using Swift, which InMobi noted was a remarkable share given that it is a new language.

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