Tech giant Apple has forced developers of apps with chance-based features to publish how likely users will receive prizes.

This followed changes to its iOS App Store rules on Wednesday.

Called "loot boxes", the features are random rewards that can give game players benefits or extra features in a game, such as abilities or playable characters.

They have been controversial in the gaming industry for their similarity to gambling, and the new rule means that every time a user buys a loot box - whether with real or in-app currency - they will know their odds of getting a prize. In May, game companies in China were required by law to disclose the odds of receiving items from loot boxes.

Singapore game developers The Sunday Times spoke with approved of Apple's move, although outside observers were less supportive.

LambdaMu Games chief executive Ivan Loo said: "There are companies out there that leverage on the gambling tendency a loot box system enables, and that's bad because you don't want a person to spend beyond his means.

"A lot of loot-box design has been unregulated to the point that a game developer can use casino tricks to get people hooked."

One of Mr Loo's games has a loot-box feature. He does not yet know how exactly he will display the odds and is waiting for further news from Apple.

BattleBrew Productions co-founder and strategic director Ian Gregory Tan said the rule change targeted the game studios that take advantage of people with addictive personalities, as well as children.

The unpredictability of loot boxes stimulate the production of a biochemical in the brain called dopamine, which is linked to rewards and motivation, and therefore can make loot boxes very addictive, according to Mr Michael David Thompson, a lecturer at DigiPen Institute of Technology's game software design and production department.

Psychologist Daniel Koh was critical of the move. "The rule change doesn't make much difference because addicted people will already know they are getting something. Without advertising the odds, you already have addictive behaviour.

"The only thing that can stop someone from being addicted is limiting access to the game," he said.

Mrs Molly Tan, a parent with a 15-year-old son and 24-year-old daughter, also did not support the rule change.

"It either doesn't make a difference or makes addiction worse because people can now calculate their chances."