https://noir-lang.org/docs/assets/js/7d7157fe.6e50af8c.js

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1const o={title:"Logging and Panics",description:"Learn how to use the println statement for debugging in Noir with this tutorial. Understand the basics of logging in Noir and how to implement it in your code.",keywords:["noir logging","println statement","print statement","panic","debugging in noir","noir std library","logging tutorial","basic logging in noir","noir logging implementation","noir debugging techniques","rust"]},a=void 0,l={},c=[{value:"<code>panic</code>",id:"panic",level:2}];function d(n){const e={code:"code",h2:"h2",p:"p",pre:"pre",...(0,s.R)(),...n.components};return(0,r.jsxs)(r.Fragment,{children:[(0,r.jsxs)(e.p,{children:["The standard library provides two familiar statements you can use: ",(0,r.jsx)(e.code,{children:"println"})," and ",(0,r.jsx)(e.code,{children:"print"}),". Despite being a limited implementation of rust's ",(0,r.jsx)(e.code,{children:"println!"})," and ",(0,r.jsx)(e.code,{children:"print!"})," macros, these constructs can be useful for debugging."]}),"\n",(0,r.jsxs)(e.p,{children:["You can print the output of both statements in your Noir code by using the ",(0,r.jsx)(e.code,{children:"nargo execute"})," command or the ",(0,r.jsx)(e.code,{children:"--show-output"})," flag when using ",(0,r.jsx)(e.code,{children:"nargo test"})," (provided there are print statements in your tests)."]}),"\n",(0,r.jsxs)(e.p,{children:["It is recommended to use ",(0,r.jsx)(e.code,{children:"nargo execute"})," if you want to debug failing constraints with ",(0,r.jsx)(e.code,{children:"println"})," or ",(0,r.jsx)(e.code,{children:"print"})," statements. This is due to every input in a test being a constant rather than a witness, so we issue an error during compilation while we only print during execution (which comes after compilation). Neither ",(0,r.jsx)(e.code,{children:"println"}),", nor ",(0,r.jsx)(e.code,{children:"print"})," are callable for failed constraints caught at compile time."]}),"\n",(0,r.jsxs)(e.p,{children:["Both ",(0,r.jsx)(e.code,{children:"print"})," and ",(0,r.jsx)(e.code,{children:"println"})," are generic functions which can work on integers, fields, strings, and even structs or expressions. For example:"]}),"\n",(0,r.jsx)(e.pre,{children:(0,r.jsx)(e.code,{className:"language-rust",children:'struct Person {\n    age: u32,\n    height: u32,\n}\n\nfn main(age: u32, height: u32) {\n    let person = Person {\n        age: age,\n        height: height,\n    };\n    println(person);\n    println(age + height);\n    println("Hello world!");\n}\n'})}),"\n",(0,r.jsxs)(e.p,{children:["You can print different types in the same statement (including strings) with a type called ",(0,r.jsx)(e.code,{children:"fmtstr"}),'. It can be specified in the same way as a normal string, just prepended with an "f" character:']}),"\n",(0,r.jsx)(e.pre,{children:(0,r.jsx)(e.code,{className:"language-rust",children:'  let fmt_str = f"i: {i}, j: {j}";\n  println(fmt_str);\n\n  let s = myStruct { y: x, x: y };\n  println(s);\n\n  println(f"i: {i}, s: {s}");\n\n  println(x);\n  println([x, y]);\n\n  let foo = fooStruct { my_struct: s, foo: 15 };\n  println(f"s: {s}, foo: {foo}");\n\n  println(15);       // prints 0x0f, implicit Field\n  println(-1 as u8); // prints 255\n  println(-1 as i8); // prints -1\n'})}),"\n",(0,r.jsxs)(e.p,{children:["Examples shown above are interchangeable between the two ",(0,r.jsx)(e.code,{children:"print"})," statements:"]}),"\n",(0,r.jsx)(e.pre,{children:(0,r.jsx)(e.code,{className:"language-rust",children:'let person = Person { age : age, height : height };\n\nprintln(person);\nprint(person);\n\nprintln("Hello world!"); // Prints with a newline at the end of the input\nprint("Hello world!");   // Prints the input and keeps cursor on the same line\n'})}),"\n",(0,r.jsx)(e.h2,{id:"panic",children:(0,r.jsx)(e.code,{children:"panic"})}),"\n",(0,r.jsxs)(e.p,{children:["The ",(0,r.jsx)(e.code,{children:"panic"})," function halts execution with an error message. It is auto-imported via the prelude, so no ",(0,r.jsx)(e.code,{children:"use"})," statement is needed."]}),"\n",(0,r.jsx)(e.pre,{children:(0,r.jsx)(e.code,{className:"language-rust",children:"fn panic<T, U>(message: T) -> U where T: StringLike\n"})}),"\n",(0,r.jsxs)(e.p,{children:["The message can be a string literal or a format str

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