The High Court, in a test case, has dismissed a woman's bid to use WhatsApp messages from her former husband before he died, to support her claim that he had wanted all his Central Provident Fund (CPF) money to go to their two sons.

Justice Valerie Thean made clear the CPF Act prescribed that a member's funds must be bequeathed through nominations or distributed via intestacy laws.

"Parliament has set out statutory boundaries for the use and transfer of CPF moneys," Justice Thean said in decision grounds issued on Monday. No party was named in the judgment.

"The father, after proper consideration, decided not to make a CPF nomination in favour of his sons. The evidence shows that he intended a specific sum in cash as part of his provision for his sons," the judge added.

The father died of pancreatic cancer on Feb 5 last year. He was 49 years old. Under intestacy laws, his widow would get half of the $718,912 in his CPF account and his two sons, 25 per cent each.

The man had divorced his first wife in December 2014 and married his second wife in March 2015.

His sons, aged 15 and 10, had applied to the courts, via their mother, for the entire CPF amount. They contend the series of WhatsApp text sent to her on Dec 29, 2016, coupled with his actions to withdraw the CPF monies, showed they were entitled to the full sum.

The ex-wife, represented by lawyers Mirza Namazie and Ong Ai Wern, claimed the CPF money, placed with the Public Trustee, are the subject of a trust and the sons are the beneficiaries.

She wanted the High Court to issue a declaration for the Public Trustee to pay out all the CPF monies to her as she is the legal guardian of their sons.

She argued that the WhatsApp conversation she had with her ex-husband about five weeks before he died showed the CPF money belonged to her sons in equity, relying on the maxim "equity treats as done that which ought to be done".

The ex-wife pointed out that his application to withdraw CPF funds on the same day as the WhatsApp conversation, coupled with his doctor certifying he was terminally ill and had Stage 4 cancer, showed he wanted to transfer the beneficial interests in the account to the sons, among other things.

But the dead man's widow, defended by lawyers Aye Cheng Shone and Derek Choo, countered that the CPF Act does not allow the creation of any trust, as claimed by the ex-wife.

They added that the WhatsApp conversation showed the father did not intend to create a trust but to provide about $500,000 for each of his children, which he did.

Justice Thean ruled the equitable maxim did not apply based on the facts and that the CPF Act also does not allow the setting up of a trust.

The judge also said the WhatsApp conversation showed he planned to withdraw his CPF funds on medical grounds to give him flexibility on how the funds were to be used.

He had applied to withdraw the funds on medical grounds on the same day of the conversation. He died about 10 days later and the judge held he would have known his CPF money would not have been paid out to him when he made his will in the early morning hours of the day he died.

The judge said his omission to deal with his CPF money in his will showed he knew the CPF Act did not allow him to do so.