There is a genre of memoir currently prevalent that is rather more self-indulgent meandering around the pointless and irrelevant than it is either memoir or significant in either historical or literary terms. And it is hard to define what raises a book out of this particular kind of mire, and makes it gentle, nostalgic, and immediately appealing. But whatever it is, Patricia Boylans Gaps of Brightness has it.

The book is the story of a life well lived, and still being lived: Boylan is in her 90s. In some ways that life has been totally unremarkable, the kind of progress, it would seem, that might have been experienced by thousands of young women with spirit, intelligence and a modicum of courage for life. Yet in other ways the life described is quite remarkable. And that is because the writer seems always to have been intensely aware of her experiences: there is an existential quality to every simple anecdote that, combined with an admirably spare quality in the writing, adds up to a needle-sharp evocation of the evolving patterns of middle-class urban life in Ireland from the early 1900s to the present day.

Patricia Boylan was born in 1913 in Coalisland, Co Tyrone, the 10th of 12 children. She left it as a small child, so it remains in her mind only as a dream place; but she sees no reason to question the description she was given: the Venice of the North. That is the quality which imbues Boylans vision. She can transpose herself into the mood and time of what she is describing, as when she says of her jet-beaded grandmother: "I don't remember when she died, but she lives on in a picture in my head of a little black figure with a halo of glitter, arms flailing in rings around her." It is essence that concerns this writer, whether in a jumble of the isolated incidents which are edited versions of pieces published or broadcast many years ago, or the more integrated chronology of her own adult life.

The descriptions of growing up in Dungannon (where the family moved when she was a toddler) are reminiscent of a Lennox Robinson play: the young Patricia Clancy sent to Coventry by her posh cousins the Corrs because she had been ordered to dance with "wee Pat McRory" at a party, and instead danced the entire evening with the tall (and handsome) sons of the local chemist whom the cousins had reserved for themselves. There are shades too of the women for whom housekeeping and cookery were an occupation so fulfilling as to amount to an art form, as she describes her mothers ingenuity in stretching a tight budget to feed a large family. In these days, when even stay-at-home wives refuse to find the time to cook anything from scratch despite every labour-saving device known to humanity, Boylans descriptions of her mothers myriad ways of presenting different kinds of potato dishes as a full (and delicious) meal are both shaming and mouth-watering. She even describes with matter-of-fact precision the different types of potatoes used: Kerrs Pinks for mashing, Records for quick roasting, Queens for ordinary roasting, and Golden Wonders only for "special": they were expensive. It seems to have been no accident that when Patricia Clancy married and became Patricia Boylan she became a both a master cook and a self-sufficient vegetable gardener.

But that was in the future for the girl from Dungannon. First, she and her small friends were to learn a love of theatre from playing at acting in the magical basement storehouse of McAleers Hotel. They wrote their own plays, based on an imaginary "Mrs S" who languished on a sofa coughing her life away, sometimes to be saved by a sailor sons magical remedy traded with pygmies in a far-off land, at other times to expire in the arms of her loved ones who returned "just in time to say farewell".

Then came a move to Belfast, where her father ("who drank") became an even more shadowy figure, and where, one gathers, money became even tighter, although her mother never complained. And it was in Belfast that the young Patricia learned about the Abbey Theatre company from reading about it in the Belfast Telegraph and the Irish News. Instantly, she decided she wanted to be an actress; and she began by presenting herself at the local theatre in the persona of a journalist, demanding to interview that nights leading actress Eileen Crowe. Standing in the wings, she saw May Craig operating as the nights prompter, and the nights stage manager showed her through the dressing rooms: he was Arthur Shields. In a few lines, Boylan manages to invoke those shoestring touring days when "the Abbey Players" were very much the servants of Yeats and Lady Gregory, and "knew their place".

The Clancy parents, however, had other ideas, and Patricia went to Leeds, where she joined her sister Mena as a trainee nurse. She spent the years 1932 to 1936 there, before returning home to persuade her parents to move to Dublin, and the environs of the Abbey Theatre. In a house on Clonliffe Road, with a thrush singing in the tree outside her bedroom window, Patricia knew the Abbey was only a tuppenny bus ride away. Accepted as a student at the Abbey School under the tutelage of Lennox Robinson, Boylan was learning, she writes, that "life is full of alternatives". It seems to have been her guiding light even then, because already she was writing about her student experiences to fund her fees. When Yeats asked to meet her as a "promising student", he eyed her, she recalls, said, "I understand you are from the North," then waved her languidly away.

It was after she became a founder member of the Dublin Verse Speaking Society, contributing regularly to the then Radio Eireann along with such luminaries as Austin Clarke and Eithne Dunne, that she met her husband, a senior administrator in RTE, who apparently fell in love with her voice and determined to meet her. On their second date he had sold the car with which he had originally impressed her. He was, he said, saving up to get married. They married a few months later.

And as Mrs Henry Boylan, Patricia began another life, one that many women would consider one of relentless toil, as she and her husband became self-sufficient from their large wartime garden, "pruning, feeding, spraying, weeding, mulching, and harvesting". They also kept hens and ducks, while they logged their own wartime fuel from the orchard, which she got to burn by kneeling for hours, scraping candle-ends onto sheets of newspaper.

In the intervals, she continued to write and broadcast, have and rear her children, and (one reads between the lines) be an emotional support to several members of her family whose lives had not been as fortunately fulfilled as her own.

Joy and positivism ooze from this infectious book as hardship and loss are dismissed with humour, and memory becomes the lamp that casts a glow on the past. Patricia Boylan seems to have been fiercely in tune with life, expecting much but never grieving when her path twisted into different channels. The result is an enchanting memoir of a life lived with generosity and hope, and a fearless optimism. You know in the reading that there were hard times for Patricia Boylan, but she makes the accounting of them a means of joyous sharing. If her spirit could be bottled and sold along with copies of her book, it would make for a matchless life-skills kit.

The book is brilliant and once you start it, you wont want to leave it down.